Like many other web developers on the Mac, I use Parallels desktop 3.0 on the Mac. I go back and forth between Boot Camp and Parallels depending on what I am testing.
I ran the most recent Windows update on my version of Vista while I was in Boot Camp. Now when I try to start Vista in Boot Camp, I get a Genuine Advantage error, and Vista will not continue to start. I have to restart in Boot Camp, and re-enter the serial number. I am running Vista Enterprise which allows virtualization.