Here's an easy place to start: detection of plagiarism. I think Joel Spolsky said something about SEO spammers copying content from stackoverflow then editing it to be search engine optimal and posting it without a link back. It seems feasible to detect this situation and actually exploit it!
It should be possible to 1) extract the optimizations and make them available to the original site and 2) start bringing the legal hammer down on the SEO spammers for violating the terms of service of sites like stackoverflow.
It should be possible to 1) extract the optimizations and make them available to the original site and 2) start bringing the legal hammer down on the SEO spammers for violating the terms of service of sites like stackoverflow.