I actually use VirtualBox when I'm running Dynamips (it has good hooks when launching network connected clients) - but for day-day productivity, Windows 7 Unity

I actually use VirtualBox when I'm running Dynamips (it has good hooks when launching network connected clients) - but for day-day productivity, Windows 7 Unity Mode in VMware is pretty great. I can double click on a .vsd file and have it launch in Visio as a close-to-native app. Also, (and this may sound stupid, but it's handy) the little "Double-Arrow Start Icon" on my Menu Bar is handy for launching Windows Apps. On my Windows Desktop System I use VMware Workstation because it reliably shuts down and restarts my linux guests, without me logging in to windows. (Though it took me a while to find out out how to do that). I.E. on a windows restart, VMware workstation gracefully shuts down the Client Operating System, and after reboot (and prior to me logging into the Windows Environment - I.E. Before I get to the office) - it restarts VMware Workstation service (not the app), and then restarts whatever Linux Guests I've selected in the "Shared VMs" panel. This is important, as my Windows 7 Desktop System is now being rebooted by Microsoft two-three times a month for security updates - which I'm fine with as long as my Linux guests are there when I want them.