LB and RB switch between home / social / video etc..
On your "my games" this will page left, and right respectively. Handy for quickly getting to a game when you have over 100 on the console like I do.
Now, if you are on something like the "Storage Devices" section of the System menu, you can instead use LT and RT to quickly scroll up or down your list of games, again this is handy to get to whatever it is you are deleting, or copying, quicker.
Finally, here's a backdrop you can use to bring back that good old green you remember from NXE or earlier... :)