Except the game doesn't pause (when you hit the PS Button). It's the same as the Xbox logo on the 360 gamepad. You just don't notice it as much because the default screen is opaque
Actually when you press the Xbox Guide Button the game does pause and the Xbox Guide menu slides out. If you pressed it when a toast(message, achievement, friend notice, etc) popped up, then it will open the appropriate part of the Guide menu.
Tommy McClain