In today's episode of DSLR Film Noob (complete with a new intro) Deejay goes more into depth about this alternate camera firmware that give you some really great features. Zebra stripes and audio level control would be enough for me to install this (if I owned a t2i), but there is a ton more of good stuff here. I really like the ability to set thresholds for zebras. That is something I've never seen on any camera.
The wiki page on what Magic Lantern is and how to install it can be found here.