http://www.shacknews.com/article/74255/unreal-engine-4-tech-demo-video-shown-off
Some interesting lighting tricks, and the discussion on how the dev tools work from other sites is very interesting as well.
The tech demo video was pretty amazing:
http://youtu.be/MOvfn1p92_8
Watching a guy play a game, make some editor changes, jump to Visual Studio and then go back in the game in real time was very cool!