i dont know about it helping the physical aspect, but certainly it will help the mental build up of pieces. like the other guy said, memorization. you dont need a keyboard straight away to memorize. obviously the keyboard becomes the essential 'other half' of the memorization, but you can do most of it either in your head visualizing, or playing on your knee, or yes stevie on your girlfriend. Im not saying this is an acheivment (im sure most of you have done better than me, this is just an example), but i learned a page of chopin etude 25/1 during the scenes of a theatre show that i wasnt involved. i got home, and i was able to play it to a reasonable speed without mistakes.
so i think it is great for the mental aspect, but i really cant comment on the physical advantages or disadvantages.