For example, if you click through to a search result from MySidekick, and then come back to the search engine after a long while, MySidekick will assume you're returning from a successful foray and thus a good recommendation. If you click to a result and come back quickly, it'll assume it was a poor recommendation. Good results move up to the top of the page in the "People's Choice" section.
Users can also suggest their own results for search queries, which go into a separate section at the bottom of the search pages (and that can later move up if users like them).
The engine has other tricks that let it take successful results from one query and apply them to others, by understanding when a user is simply modifying his or her terms and searching again to get better results.
This is an interesting blend of algorithmic and user-powered search, sort of a Google meets Del.icio.us. I find it a bit more conceptually complex than I'd like, and looks like it could be hacked or gamed, but the team is on to something interesting.
MySideKick is in private beta, but the CEO told me that the first 100 people who use the referral name webware at the sign-up page will get access. If you try it, please let others here know what you think.