Did you know that when a bullet richochets, its angle of exit is generally less than the angle of entry? That is, after the bullet strikes the surface, it winds up on a new trajectory that runs almost parallel to the surface it impacted. This is unlike say a bouncing ball, that will exit at about the same angle as it entered.
This is worthwhile knowledge to have, as it has both offensive and defensive implications.
Watch this video, starting at about 3:36:
Consider the implications, both offensively and defensively.
(h/t Gabe Suarez)
Stuff From Hsoi 
I first read about this in Black Hawk Down. Apparently the Delta boys had to tell the Rangers to stop hugging the walls as there were rounds traveling along them.
Exactly.