Hihi, found test render of an earlier version of the engine, with placeholder art stolen from google somewhere, and a really hacked together ball particle engine:
http://www.mojang.com/notch/chambered/bounce.gif
The engine supports rendering to disk at 30 fps regardless of actual framerate. If you’ve got lower fps than 30, it’ll still render (exactly) 30 fps to disk. The game will obviously run at lower than normal speed when that happens, but playing back the video will show it at full speed.