On dual or quad computers, parallels only uses a single CPU, so in some respects it's not great. However, I do like the fact that I don't have to reboot my system to use windows and I can drag and drop things from one environment to the other.
We tried to use Parallels on my wife's MBP for a stitching application, but the USB device wasn't recognized by it's software. Parallels knew it was there, but for some reason their software couldn't read the device. I ended up putting bootcamp on it and all has been well since.
VMware's product looks very interesting, but I don't know anybody using it, so I can't comment on it. Maybe they support FW and dual/quad cores, I haven't been able to tell.
Wayne