Yahoo announced Instant Search last night (more info on this landing page).
Like Google Suggest and Snap, Yahoo has added ajax functionality to search.
It’s different, though. Google Suggest and Snap use ajax to suggest search queries based on what you’ve typed in so far, whereas Yahoo has integrated basic search results into the interface. This means you can get answers to simple and popular searches (like weather) without a page refresh.
Try it out. Yahoo suggests queries such as “Boston Weather” and “Wikipedia”. This type of search gives good results.
And Yahoo takes a small swipe at Google by saying ““Why feel lucky when you can be right”, a reference to Google’s Feeling Lucky button. John Battelle says “Meeeeyowww, the claws are out….” :-)
Additional Reading
Charlene Li, Google Blogoscoped, Brad Hill, Ken Leebow, Search Engine Roundtable