Skitty, like Pieplup said, the O-powers can be used to hatch eggs faster, buy items cheaper (bargain power), gain more either EXP or prize money in battles, make it easier to catch, encounter or avoid wild Pokemon, and HP and PP restoring power. But they will only last for a few minutes, and then you need to wait a little before you can use them again. They'll also level up the more you use them. They can be very handy; I've mostly used the EXP and prize money powers myself.
Turtwig