Just be prepared to treat the VM like another computer.
The snapshot features is pretty decent. Though I like the way virtual pc does it better. As it actually makes sense there.
They come out with new versions about once a month. Which is usually when I update all of my base snapshots with all the latest patches and recompress the empty space.
The speed is decent. Though VMWare is a bit faster in general but not much so that you would notice.
The directx support is about as good as what you will find in wine.
But it is pretty cool to be able to totally jack up a computer and with a few clicks it is back to normal. I use them quite a bit to see if I like a piece of software enough to actually use it on my main computer. Media monkey is the one up for today
Probably my biggest tip is to keep the vhd's defragmented. They fragment pretty quickly. Just defragmented one today and it had like 2000 fragments. Defragmenting inside of the vhd is not as important but it helps when you are removing extra space. I usually use something like mydefrag then sdelete.
Oh one thing I have noticed is the guest additions do not install very well. So do not put them in your main snapshot. I usually keep 2 level snapshot. One with and the main one that is derived from that does not have it. I have had on many occasions the additions just not install properly. One of my XP installs right now is messed up because of it.