I have UDK, I've browsed around in it a bit, but haven't really used it for anything yet. If anyone ever gets seriously interested in it, as in ready to put the time and effort into making a serious game, let me know, and we can either work together, or just work separately on individual projects, but ask each other questions. I have my own game idea, but I'm not really going to take the enormous time required to make it in UDK unless there is some additional form of motivation.
To everyone thinking about using UDK: you have no idea how much work it requires. You need expert coding skills, modeling skills, and an advanced knowledge of 3D environments and effects.