[edit] Does it hurt?

Yes and no: Usually it stings for a second or two. It's comparable to being snapped by a rubber band. It also depends on how much clothing is on you, because more clothing provides padding for the impact, meaning less pain. To keep the sport fun, all good paintball fields regulate the speed of paintball guns. The speed is always 300 FPS (Feet Per Second) or lower, which has shown to be a safe standard speed.
After getting hit by a paintball, the spot of impact will usually form a ring-shaped welt although some places such as the thigh may form minor bruises