Today we went through a lot of demos and labs. The most impressive was the "Upgrade" demo. We had a test cluster that was a version behind. The instructor dropped a tar file on one of the nodes, ran an upgrade command from the command line and a couple of minutes later... BAM! All three nodes in the cluster were updated with no down time. The only instance where the nodes would have to be rebooted is when there is a change to the kernel. They have a service that migrates the change to the other nodes so you don't have to.
All in all it was really cool and I can't wait to get to play with ours. If they give me access. :)