If you've ever traded or sold links on a forum, you may soon be penalized for it. Microsoft has recently assigned a patent that will streamline this penalty by actively combing forums for people (from here on out referred to as "spammers") who:
...log onto SEO forums to communicate with each other for trading links, including link exchange, link sale, and recommendation link exchange. These forums are increasingly more popular. Spammers post requests for "link exchange", "buy & sell link", and "recommendation exchange" in these forums, along with the URLs of their websites, and other interested spammers may reply the requests and provide the URLs of their websites.”.

The patent designation is:

Forum Mining for Suspicious Link Spam Sites Detection - Microsoft - Filed; Feb. 06 2008 – Assigned; Aug. 06 2009

Has this piqued your curiosity? If yes, Huomah has outlined some of the potential impacts of this action, complete with flowcharts :

Are the search engines spying on SEOs? - SEO and Internet Marketing blog, news and views

NOTE: Many search engine's already penalize you for buying and selling links. This would just be another way to automate the process.