I do freelance bookkeeping and payroll for a number of clients, and the old PC I was using for work finally gave up the ghost. So I decided to get VPC instead of a new PC, as I really prefer my Mac, and financially it made sense. The program I'm using VPC for is Quickbooks Pro 2004.
My computer: Rev. A Flat-Panel iMac, 800 Mhz G4, 768 MB RAM, OS 10.2.8
The installation was incredibly smooth and fast, which pleasantly surprised me. By default, VPC wants to install Windows in your Documents folder, which seemed bizarre to me, but I installed it in the Applications folder with no complications.
Things started to slow down after that point. Setting up Windows took *forever* (as at that point I was on the "virtual" machine, which for me runs at 233 Mhz). The good news is that when you finish a session in VPC, the program saves Windows' state (as if it were hibernating), so the next time you don't have to go through the interminably long process of waiting for the virtual machine to boot.
I encountered trouble when I tried to print to my HP 920c, which is a USB printer. After doing some googling, I realized there is an update patch to VPC (7.01) and after installing it, printing works fine.
As for using Quickbooks, it's really quite responsive and I have no complaints. It's easily as fast and stable as it was on the 5-year-old PC I was using, if not moreso. I think the key to VPC is being realistic about what it is and what it's intended to do. For my purposes, it's perfect!