Those of you who haven't been paying attention might have missed the fact that Macs now have Intel processors in them. This means that they can run Windows without ugly, slow CPU emulation. Instead, you can use Boot Camp to boot the machine directly into a separate Windows partition, or you now have a choice of two competing commercial virtualization offerings: Parallels Desktop and VMware Fusion.
I've been using Parallels for some time now. They certainly have gotten more right than wrong, but although Fusion is late to the party (and it isn't even released yet), I have to say, their initial offering is a very, very strong competitor with the more mature Parallels product.
Suspending and resuming virtual machines in Parallels has always been a sore spot for me. Though the screen will pop up quite quickly, the entire machine - both the host and guest - seem to be mired in a tar pit for a very long time while the virtual machine pages itself in. During this time, you really have no indication of what is happening or how long it might take. Perhaps this has more to do with the fact that I use Mac Minis that have slow disks, but even so, it's an annoyance.
The only other real difference of any consequence I have found so far is when using the Netflix Watch Now movie player. Under parallels, rapid motion and panning camera shots often show ugly visible "tearing" artifacts. This is likely caused by a lack of synchronization between the vertical refresh interval of the monitor and the virtual graphics card in the guest. Fusion doesn't have this problem. The netflix player in full screen looks and acts, to my eye, exactly like it would running under Boot Camp.
The other sore spot is converting from one to the other. Although you'd really only likely ever have to do this once, so far as I am aware, in both directions it is a byzantine arrangement involving installing a special Windows program in the opposite software's guest and having it write out the disk contents to a network share. Ugh. Even then, there are a couple of added annoyances. VMWare's virtual machine supports ACPI. The Parallels one does not. There is no way to switch Windows XP from standard to ACPI, so you wind up with no MP support and other quirks until/unless you reinstall Windows. Plus, the Parallels tools won't de-install unless you run the deinstall from within Parallels. There's no real harm in leaving the tools there, but you can't get rid of them.
I took VMware up on their pre-release pricing offer and bought a license. At the time, I figured I was just donating money to a lost cause. Parallels had such a lead, it was hard to imagine VMware being able to catch up. Boy, was I wrong. Now we've got a horse race. And the real winners are mac users who are surely going to benefit one way or the other.