Well, I take mine mountainbike riding and it has never skipped once yet.
Should I throw in the real 40hrs playback (if using Atrac3, about 30hrs for mp3 files)
I believe this will cache up to 60 seconds of music in a split second, so unless you are throwing it at walls nonstop it shouldnt skip. I will however admit I havent been running with it, so I dont know how it would cope with the constand shocks of running, however I would have expected MTB riding to put more strain on the player than running.