I've noticed when plugged into power (such as my jbl speaker dock) that it charges just fine while playing. I was kinda surprised when I saw this, actually. Just today, I put my almost dead ipod on the jbl dock and was playing music from it to test out the capability of the speakers (just got it yesterday), and by the time I was done, and needed to head to work (after a few hours of playing), I grabbed it from the dock, put it in the rhinoskin case and set it down. Then I noticed it was reporting the battery was 100% full (it was no longer displaying a charge status).
Perhaps there is a usb mode, command, or signal that tells the port to push more power rather than the device pull more power? Of course, the usb stuff really isn't working altogether yet so this is something that is not likely to be fixed until usb is working.