After google, google toolbar, gmail and countless more exciting pieces of software... Google comes along with Google Desktop - Just plain amazing, and wroks seamlessly with all the other stuff they offer...
What can I say, I'm so waiting for GoogleOS! I will buy it the minute it is available. I have never seen such cool things. It searches in your Email, IM chats, Cached web pages, and documents. The only thing I would like is more configuration options (were to search, run index again) but I guess that to make it really dummy proof they had to do it this way.
Run and download!