I use VMWare Fusion primarily to run QuickBooks on Windows XP. I also use it for the occasional BreezeBrowser and ProShowGold session. Here's a video that shows me launching Fusion on a MacBook Pro, opening and resuming a virtual machine (QuickBooks is open), starting IE7, switching to Unity mode (like ||'s Coherence), and tabbing between Mail.app and the apps in Fusion. Finally, I go back to Single Window mode, suspend the virtual machine, and quit Fusion.
Anyway, the point is to show that when cached, resuming a paused virtual machine is REALLY FAST. In general, I don't even notice that I'm running Windows in a VM except when I drag windows around (refresh is a bit slow). It's the perfect blend of Mac (99%) and Windows (1%).
The video here actually looks like it's running the fast side. That may be a result of the conversion from Quicktime movie to Flash.