Well, I installed the google desktop search and within an hour used it to find a document I was sure I had, but couldn't find. Then I used it to find the email with the link I used to download a video several months ago.
I think it will be quite useful, and after monitoring it's progress it seems to use almost zero cpu when you're using the computer, and not a whole lot of memory either.
I'll have to see if it remains nice though.