VirtualBox is free / open source: http://www.virtualbox.org/

From the site: Runs on Windows, Linux, Macintosh and OpenSolaris hosts and supports a large number of guest operating systems including but not limited to Windows (NT 4.0, 2000, XP, Server 2003, Vista), DOS/Windows 3.x, Linux (2.4 and 2.6), Solaris and OpenSolaris, and OpenBSD.

On this site, you can find sources, binaries, documentation and other resources for VirtualBox. For up-to-date press coverage about VirtualBox: blogs.sun.com/VirtualBoxBuzz

If you're going to use fusion, you'll probably not want to go with 1GB of RAM which is what you get with the last-gen macbook. That's another reason to consider getting the new one, or alternatively you could get a memory upgrade - but be sure to get it from a third party seller like crucial, not from Apple, to save money.

I have no trouble with Fusion, except for playing some old games, but I have 4GB RAM. I'm not sure if the 2GB you get with the new MacBook is enough.

It feels (I haven't done any benchmarks) snappier than parallels, and is more efficient with memory. I'll buy buying a copy at the end of the trial. YMMV.

I've been happy with it. I've run a variety of operating systems on it, and haven't run into any problems. Other people's mileage may vary compared to mine.

If you want to comparison shop, Parallels and VirtualBox are also options. Others I know have been happy with both, but I haven't played much with either.

VMWare fusion is great. I received a copy from a recruiter, which came in handy when I took a course that required Quartus (Windows or Linux). I had no issue interfacing with the CPLDs we were using (I used XP).