Five Runs (silly how many Ruby/Rails-oriented companies are named with two words and one with a number) developed a social load testing solution that appears to help you load test your site and trace bottlenecks in code, but instead of pounding on your own site using local automation, it allows live visitors -- fellow developers who need load tests done for their sites -- to pound on your site.
http://www.fiveruns.com/products/tuneup
Interesting concept. We even have social networking for load testing.. LOL..