Ask yourself this question: "which is easier to find, webpages on the web or files in your computer and local network?"  For me, its the webpages thanks to Google.  I suspect same answer applies to majority of computer users.  My 30 gig drive is 90% full, but I don't know why.  I lose track of files almost as soon as I store them.  Sure, I try to organize them, but I forget about why, how, and where things are organized.  If my disk is a giant tree, I am a forgetful squirrel that was a bag lady in a previous life.

I do use Windows' search feature, but its too slow and just doesn't seem to get me what I want.  What I want is something that works as fast and as simple as Google for things on my machine.  Obviously, many people had similar thoughts, but I have yet to see a solution that satisfy my needs.