Wow, I'm surprised you just barely heard of it now. It's not anything like the wiimote, but something such as tossing yourself and the controller forward might make one of your characters do a roll forward. Fishing, pulling the controller and yourself back might help you pull the reel harder when pressing down or that button isn't working. etc.. Not full sensitive with pointing and what not like the wii's.
I dont know why sony put this new feature to ps3 control. Compare it to 360 and wii's control. Its in my opinion wrost of all the new gen controller. For 360 I get the good old shaking and for wii I get the real motion senser and for sony lol i get half of the motion senser wtf.