Differences between desktop/laptop video card of same type?

What differences will i notice while gaming between a GeForce 8 video card for a desktop, and the same model for a laptop?

(example: if my desktop has a GeForce 8600 GT and my laptop has a GeForce 8600M GT [Both 256MB video cards], what differences will i notice, if both desktop and laptop have the same processor, RAM, and video quality settings)|||the same