We've been using this in house for about 2 months now -- it saved us from the only qualm we have with OS X software... quickbooks. Ridiculious that their Mac version is still years behind their PC version, and while we are looking to replace it completely because of our disgust, we swung our accountants over to the PC version, running on an iMac dual monitor setup.
I got to say, it's been pretty painless except:
1. MS office programs saving directly to 'shared folders' will crash the shared network, and you can't access it again until a PC restart. The fix is to save any office file to another location and do a drag and drop.
2. USB printers don't connect directly -- we've used the paralells recommended: share the printer on the mac side, install windows bonjour, add the printer using a generic driver, and it works just fine.
All in all, it's beautiful, and a much better system then when I had to use Virtual PC back in the day. I look forward to using it further in our web development tests... but that's about it:)