In reply to:
Personally, I think that the S30 is going to usurp my iPod as the player that I take to the gym
Hmm, what makes you say that [apart from being loyal to the prodicts you help create - which is not to be ignored either]?
I would have thought that the iPods ability to store more music would be more useful, than the 3 hour or so playback in the S30.
Perhaps you have a more rigourous gym routine tha some of us and thus the solid-state nature of a MMC/SD playback device is a deciding factor?
I would also imagine that the lower cost [and possibly weight] of the S30 may also contribute - lower weight is obvious if you wear it while exercising, although strapping some really heavy early Rio players around your wrists and ankles could be a way of adding the extra level of difficulty to your workout.
Lower cost - well if you drop it or it gets dropped or stolen, then its cheaper to replace than a iPod. And of course, if the company gives you one for free then that helps too when it comes to replace it.
Interesting to see also that you have a iPod, so I expect maybe some future Rio products might outdo the iPod in some areas - no doubt the UI for one.