This was tested on a fresh Raspbian Wheezy from NOOBS 1.2.1.

Minecraft Pi ran successfully and was very fast. I had to install it manually because I was using an old release of Raspbian 7 wheezy that doesn’t have Minecraft pre-installed.

RECOMMENDATIONS FOR BEST PERFORMANCE:

CLOSE DOWN ALL BROWSERS BEFORE OPENING MINECRAFT

ALL CPU AND GPU INTENSIVE APPLICATIONS SHOULD BE SHUT DOWN BEFORE LAUNCHING MINECRAFT (ie. Chromium)