I've been using VM Ware desktop for a few years now, for all the reasons everyone is talking about.

-You don't have to rebuild your development stack every time you get a new machine.

-You can copy the VM to an external drive and run it on another machine in a pinch.

-You can P2V a clients machine and take a copy home with you for testing

-Upgrading or adding new tools is worry free, since you can take a snapshot before the upgrade/install. If it winds up hosing the system you can revert back and be back up and running in a few minutes. This is a biggie for me.

-Laplink PCmover works well for moving stuff from one VM to another. I recently (finally) upgraded my XP dev environment to Win 7. Laplink did most of the heavy lifting, however, it did not move MS Visual Studio. Had to reinstall with a new key for that one.

Very happy with VMs for dev work. My machine is an i7 with 12 gigs of ram. More would be better, next box will have at least 32

Mike