I can only speak for the ebony (not real ebony, just as with the teak and walnut). They feel almost like paper, and they scuff quite easily. Mine had some light marks right out of the box, which I think was from the original inside top of the box rubbing against the phone.
I was disappointed enough to send it back and stick with my woven black back.
Bamboo may be better as it is actually bamboo. Don't know what they're doing with the other finishes, but the ebony one was lousy.