I can't really comment much on the iPod part as I haven't used it much for that. I'd be listening to podcasts in the car with it, but I need an adaptor for the headset port first, since it is sunk in too far to accept most standard plugs.

Feature wise, all I did on my old Nano was podcasts as well. Comparing pure music playback to the Rio Karma, the interface is still lacking. Video is nice though on it, and I have a feeling mine will mostly see video and podcast use, with the Karma still there as my main portable music player.

I did tinker around with the On-The-Go playlist and it's kinda cool. You can add individual songs, albums, artists, or playlists to it. Then you can rearrange songs with the touchscreen. It reminds me a lot of the Now and Next setup on the Karma, clunkier. On the Karma, Now and Next was always populated, even if you were playing an album. On the iPhone, you have to specifically go to the On-The-Go playlist to get this functionality.