It's too bad, because I know other players have no problem on motorcycles. For example, my PJB-100 (with a 2.5" drive) spent the better part of a year strapped to the fairing on my bike with no padding or shock absorption, but absolutely no ill effects. If you're looking for a fairly rugged player cheap, you could get one of those for a good price since they haven't been made for a while.

I haven't taken the Karma out on the bike yet, mainly because I don't get on the bike as often since I haven't had time to fix it recently. However, even if the bike was in 100% working order, I'd be wary because of everything I've read, and would probably keep it in my jacket or something to absorb the vibrations.