The iMonk in a BHT post just made me aware that Google Desktop is finally available for Macs. I've already got it indexing my drives. Michael links to theappleblog for more informaton on the desktop product. Check it out.
UPDATE: I've been using it for a couple of days and its speed is blowing my mind. Double click the Apple key, it launches and the results appear as fast as I type. (I am running a Mac Pro.)