I'll definitely be demoing the Rift for people using UDK, glad I waited. The better graphics add to immersion more than I thought. Some fun things to try:
Open and play VCTF-Necropolis in UDK Editor. Beautiful level with alien cathedral looking architecture. I prefer it with setallspeed 0.5. You can also drive the Scorpion and fly the Manta. I've never appreciated the artistry in the levels and vehicles before. Much better 'walking around' experience than the Tuscany Demos. May require a good graphics card.
Play LSMobile_Castle though the UDK Game or Editor. It will take your control away for a minute, but ride it out. Then setallspeed 5.0 and fly. It basically feels exactly like this 'Neo flying' scene from the The Matrix Reloaded: