After a fair amount of work and collaboration, Xen is once again a functional and supported platform on CentOS and it's doing so with the kind of flare you'd expect. With articles on linux.com, blog entries, and a load of twitter feeds, the goal is to help folks migrate their older systems to the new platform.
It's not all sunshine though. For the purists, this does require replacing the stock kernel and libvirt, as well as a minor gotcha involving the bnx2 network driver. All in all though it looks pretty good, and should continue to improve as the community around it grows.
If you want to get started, give it a shot, and help us improve the project! You'll find the directions to get you going on the CentOS wiki. Congrats to everyone involved for putting this together and making it happen.