Parallels User
I currently use v3.0. I spent a while looking at Fusion vs. Parallels, and chose Parallels in the end.
I give it two thumbs up on my MacBook Pro. It's quick, works well, handles the management of resources well, and boots quickly.
Improved Copy and Paste will be greatly appreciated.
I'm not sure I'll notice the 20-30% performance improvement per se (I only use it for a handful of Applications that I can't get on the Apple) but the integration has been good. If only Quicken could catch up their software for the OS X side vs. the Windows side.
I've been told you can use Boot Camp + Parallels, so that you can launch natively into your second operating system, or as a virtual machine. Making it highly flexible. Boot for games, or boot for easy compatibility. I didn't do that, but if there is significant performance improvement maybe this won't be necessary.
I'll be looking to upgrade to 4.0 but maybe in a few months. The software has been very robust, so no fears there, but after the last few iPhone debacles, I'm more cautious than ever before. Even from software vendors I trust.