I've gone back and forth in the past between MSN Desktop Search and Copernic.
One of the reasons I ended up sticking with MSN was the shortcut keys. Ever since I discovered ActiveWords, though, this hasn't been as important and I found myself once again gravitating towards the cleaner Copernic interface.
Unfortunately, Copernic doesn't seem to work (yet) in Outlook 2007. (Yes, search is better in Outlook 2007, but I would prefer to have my results indexed outside of Outlook too). If you have the beta installed, it doesn't allow you to specify Outlook locations.
As a result, I'm back to using Windows Desktop Search.
It's much improved since I've last used it. The new look is cleaner than previous MSN versions, although I still prefer Copernic. What I'm really liking right now is the ability to view search results in Outlook. Very well done.