I think I’m a fan of Google’s Instant Search. Rather than having to hit “enter” or click the “search” button, the search results automatically refresh as I type. It’s quirky sometimes, because I’ll see some search results that look accurate as I’v only typed in a couple letters, and if I’m typing too fast, it passes me by and it’s not always easy to back up to to those previous results. So, for the most part, I like it.
Google just introduced Instant Preview, which displays a screenshot of each search result, while highlighting the relevant part of the page that qualified it as a search result. Convenient for skimming, and could lead to some interesting hacks that websites implement to generate some catchy screenshots that may or may not look the same when you actually click the link.