I use it every day. I've got a MacPro with dual monitors. The left side runs Vista with 8 gigs of memory and the right side runs OS X with 8 gigs of memory.
On the windows side I run Flexi 8.5, Corel X4, QuickBooks, and Office 2007 without any issues. On my Mac I run the complete Adobe CS3 suite.
A lot of times I run all those applications at the same time and the computer doesn't even blink.
Version 2.0 is a free upgrade and has a couple new features and bug fixes.
I would highly recommend Fusion. I have Parallel's on my MacBook Pro and Fusion is way, way, way, better