Google Desktop is the new killer application. It's the best thing thing since Google.
It indexes your local content (e.g. Outlook, Office, etc.) and the pages you view, and integrates intuitively with Google's online search. I'd say seamlessly, but there is a seam in that it differentiates between the two result sets, as it should.
What does this mean to you? Let's say I wrote an architecture document for Project Twinkle but forget where I put it. I type "architecture project twinkle" into my Google Desktop's search box and it comes back with all the documents, e-mail and web pages related to the architecture of Project Twinkle. If I don't find what I want, I can run the same search on the web with a single click.
No more Windows Explorer searches, no more cutting and pasting search terms from window to window, heck, I might not even need Lookout anymore.
Go get it, now: http://desktop.google.com