MacTech has an article up with results of their benchmark tests of Parallels and VMWare Fusion for OS X. From the write-up:

If you want a virtualization product (that allows you to run Windows alongside Mac OS X), and you want the best performance for the types of things that we tested, then clearly you need to run XP and not Vista. Furthermore, in our tests, both VMware Fusion and Parallels performed well, and were a good user experience. That said, Parallels was somewhat faster in general than VMware Fusion for XP.

You need to read the whole article to get a feel for the nuances of virtualization options on the Mac (especially if you plan to run Vista virtualized) and it needs to be noted that they do not cover alternatives such as Qemu or products that take a kind-of hybrid approach (ala CrossOver).

Overall, there is good data to help those who haven't already invested in a virtualization solution make a fairly informed decision.

No time for a full write-up, but LifeHacker mentioned Sandboxie today and that led me to look at Altiris SVS. I've been espousing file system and registry virtualization in Vista quite a bit lately and this just kicks it up a bit.

When I get time (after my final) to play with this, I'll post a more complete review or see if SF is interested in a full feature. Meanwhile, grab the tools and give them a go!

Like many OS X users, I have Parallels installed with a number of VMs configured & ready to run at a moment's notice. I have an XP SP2 image built with Office 2003 / IE 7 and another with Vista (Business edition) and Office 2007.

Without a doubt, XP + O2K3 easily wins what I refer to as the battle of the VMs -- at least on my first-gen MacBook Pro. The XP image only requires 512MB RAM to be ultra-responsive, and I get to keep the disk caching policy set to better performance to OS X. Vista barely crawls with 900MB RAM (I started with Microsoft-stated 512MB minimum requirement) and I can go get a cup of coffee while it and O2K7 both startup. The Vista VM also requires me to give it disk priority and consumes so many other system resources that OS X is a more than a tad unresponsive at times as well.

I'm not disparaging Vista or the new Office. They both have some nice features and way more security options. When it comes to getting cross-platform work done, tho, XP will remain my primary Parallels VM until at least my hardware profile catches up.

Don't even get me started on how fast my FreeBSD 6.2 image is, tho *:^)