Harsh Consequences

It is a matter of business survival for Google (and search engines in general) to fight blackhat tactics. It can be very aggressive and hurt your rankings massively, for a long period of time.

It can take more than 6 months to recover from Panda or Penguin algorithmic penalties. They impact the whole website. A negative rating by the Panda algorithm can prevent good content on the site from ranking.

Article spinning is the practice of writing an article with backlinks and posting it everywhere possible on the Internet, usually in article directories.- Can trigger Penguin algorithmic penalties and manual actions.
Automatically generated content is about creating pages using Markov chains to generates random phrases containing keywords. It can also be copying of content found elsewhere on the Internet without adding value.- Triggers Panda algorithmic penalties and manual actions, lowers ranking of all website content on the long run.
Automated queries is about generating artifical requests to search engines and to automatically click on some search results to fake real traffic and gain ranks in SERPs.- Click rate is a noisy ranking factor, no real benefit, clicks may be ignored.
Automated submissions is the practice of systematically submitting any produced content to article directories, blogs or other websites without any editorial review.- Other websites compete with your content for ranking, can trigger manual penalties against such hosts.
Bait-and-Switch / Page Swapping consists in waiting for some pages to rank for specific keywords, then to modify their content and benefit from their ranking and traffic.- No long term benefit, links may point to off topic content leading to loss of benefits.
Buying expired domains often having a good PageRank and forwarding all traffic to a target website.- Links may not be trusted anymore and target content may be considered off topic, link benefit will be lost.
Cloaking is about showing different content to search engines and to standard users, in order to manipulate them.- Site will lose Google's trust anc can be removed from search results.
Cookie stuffing / dropping is mean to try to make a profit by creating many affiliate program cookies from a unique visit to a site. If the users visit another affiliate site, and makes a purchase, the cookie dropper get a commission although he/she did not explicitely referred the client.- Site will lose Google's trust and can be removed from search results.
Content scrapping is the process of copying content from other websites and hosting it on one's own website without authorization. It is usually performed on a massive scale.- Triggers Panda algorithmic penalties and manual actions, lowers ranking of all website content on the long run.
Domain squatting / Cybersquatting is about using a domain name of a celebrity or a trademark with the sole purpose of making an illegitimate profit on it.- Short term benefit, DMCA request can have a site removed from search results.
Doorway pages is about creating pages with shallow content answering user queries, and having them forwarded to other pages (usually unrelated to the original query).- Triggers Panda algorithmic penalties, pages are considered as spam and are not displayed in search results.
Duplicate domain with duplicate content is about creating copies of a website, using a different domain name.- Triggers the algorithm detecting those domains name (including EMDs with low value content), these are removed from search results.
Google Bombing / Washing is the practice of ranking an off-topic webpage on the top of search results by linking massively to it.- Algorithms detect massive acquisition of low quality links and remove web pages from search results, such sites are notified to spam teams and can lead to manual penalties.
Gateway pages are typically near duplicate content or thin content pages aiming at attracting users with different combination of keywords. They usually have links to only a few target pages within the site.- Triggers Panda algorithmic penalties, pages are considered as spam and are not displayed in search results.
Guest Blogging / Posting is about hosting content written by external contributors on one's blog or website. When practiced excessively, it is considered as a black hat technique.- Triggers Panda algorithmic penalties for host and Penguin penalties for target site, both can face manual penalties.
Hidden text and links are created by using the same text and background color (i.e., no contrast) or by using CSS techniques. Typically, web crawlers see content that regular users don't see.- Can trigger manual penalties.
Irrelevant keywords is about adding unrelated ranking keywords to a page's content in order to boost its traffic.- Can trigger manual penalties and Panda algorithmic penalties.
Index stuffing is about trying to index as many pages as possible in the index of search engines.- If the pages are of low quality, it will trigger a Panda algorithmic penalty.
IP delivery is a synonym of cloaking.- See cloacking.
Keyword stuffing is about filling a page's content with long lists of keywords, hoping search engines will rank it for all of them.- This triggers Panda algorithmic penalties and can result in manual penalties too.
Link farms are groups of web servers containing websites created for the sole purpose of hosting artificially generated content and links between them. The purpose is too articifially raise their PageRank, and then to create links to money making websites.- Triggers Penguin algorithmic penalties for hosting and target sites, results in manual penalties for all sites.
Link spamming is about creating a high number of backlinks in forums, on blog or other websites for the sole purpose of raising a website's profile.- Triggers Penguin algorithmic penalties and manual actions.
Link wheels is a type of link scheme involving the creation of several dozen blogs or site where one link is created towards a money site and another to the next blog or site, until a wheel is created.- Triggers Penguin algorithmic penalties and manual actions.
Link scheme is any technique used to benefit from unnatural or illegitimate links.- Triggers Penguin algorithmic penalties and manual actions.
Link exchange is nothing more than 'I create a link to your website if you create one on yours to my website'. The main purpose is to support each other's website, rather than sharing or linking to valuable content.- Can trigger Penguin algorithmic penalties and manual actions.
Mirror sites is simply copying a website multiple times with different domain names.- This is detected by a specific algorithm, such sites are removed from search results.
Malware distribution is any technique aiming at installing software or viruses on a user's PC without their consent.- Such sites lose the trust of Google and a removed from search results.
Negative SEO is the practice of creating or forwarding backlinks from low quality or penalized websites to competition websites in order to lower their rankings or to extort something from them.- Google is good at detecting such practices, sites sending such links can be manually penalized, their outbound links are automatically neutralized.
Over optimization - Some websites are optimized a little too well compared to naturally ranking websites. Title, keywords and content is crafted specifically for search engines, rather than normal users.- If this over-optimization breaks guidelines, it can result in manual penalties, otherwise there is nothing to worry about.
Over optimized anchors is about using only traffic generating or valuable keywords in the text of anchors, hoping it improves the ranking of the target pages.- This is equivalent to keyword stuffing.
Page stuffing is filling a page's content with related keywords in order to improve its ranking in search results.- This has the same consequences as keyword stuffing.
Parasite hosting is hosting a site on someone else's web server without their consent and without them knowing about it.- The host webmaster may receive a manual penalty (hacked site).
Paid links is any link acquired in exchange for money or goods.- This can result in manual penalties and trigger a Penguin algorithmic penalty.
Private Blog Networks are groups of connected blogs created and controlled by one or several individuals for the sole purpose of improving the rankings of their websites by sending backlinks from these networks.- Triggers Penguin algorithmic penalties and can result in manual actions too.
Social media spamming is the process of filling Facebook, Twitter and other social sites with comments and backlinks to one's website.- Triggers Penguin algorithmic penalties and can result in manual actions.
Spam pages are pages created with low value content or excessive advertising.- Triggers Panda algorithmic penalties and can result in manual actions.
Spamdexing is a generic name for all techniques aiming at manipulating rankings in search engines' indexes.- Triggers Penguin and Panda algorithmic penalties, together with manual penalties.
Sneaky redirects is an implementation of cloacking.- See cloacking.
Twitter automation is about systematically creating a Tweet when something happens on your site (a page is created, a new promotion is beginning...). It is equivalent to spamming on Twitter.- Such links are considered as low value, since there is often no editorial content review, or are blatantly unnatural, there offer very low to no benefits.
Throw away domains is registering domain names for a short period of time and posting content to catch traffic for a trends or a news story. For example, XXXcheatedonYYY.com.- EMDs without good content are filtered out of search engine results.
Unreadable text is choosing a font size so small regular users cannot read it, but web crawlers can.- Triggers Panda algorithmic penalties and can result in manual penalties too.
Using brand as keyword is about using a brand's name illegitimately on a website to try to benefit from the corresponding traffic.- This can trigger DMCA removal requests, such sites (or part of their content) can be removed from search results.

If you have suggestions for extra entries, put them in the comments!