I was looking at gnome3.org today, and their FAQ says that "The traditional GNOME 2 desktop will not disappear overnight, however: releases of GNOME 2 will continue to be supported by distributions for years to come." so clearly they don't imagine everyone will drop all their software and retrain all their users overnight.
Ubuntu doesn't see to have that thought, either.
I was looking for a way to run fc15 in a VM, which worked in the alpha and hasn't (for me) since. The FAQ says that's the case, no VM has a powerful enough video emulation to handle the worthless eye candy. The Virtualbox people say much the same, but their spin is that the video could do the job but GNOME insisted on using some direct to hardware stuff they don't off. I freely admit I didn't spend a lot of time deciding anything other than both of them imply the fault is with the other.
My fc13 machines are moving to RHEL6.0 or a similar distribution, I'll be able to keep them secure for a while and see which way the wind blows.