I've just upgraded Coofer Cat from Fedora 4 to FC5. It's a job that's been well over due for quite a while. It was characteristically easy to do over the network (without CDs) - I just followed someone's instructions. T'internet's great, isn't it?
Update: I've also upgraded my laptop from FC5 to FC6 - equally simple to do. Try doing that with Vista! Could this be the easiest OS upgrade ever?