Battery life is very important, and well worth keep mentioning. It's one of the "normal" specs of a music player that you can easily compare across the board and so should be one of the critical factors for purely competitive reasons, let alone better enjoyment and usage reasons! From what I hear the Sony battery life claims are never what they state on paper, although they still can last longer than most iPod batteries (on paper and in practice). I brought my girlfriend a 1Gb shuffle earlier this year and the battery life is superb, much longer than what it states it should be! It also seems to recharge itself! If you use it for a bit and it goes into orange for a while you can turn it off, leave it and it will go back to green. It will do this repeatidly on one charge!
Before you all say ye I know its not "actually" recharging! Humour me! It still has pretty good battery life in my opinion. Better than it states. I think they could make the shuffle have a huge leap in battery life very easily.
But yes, 20+ hours on the colour screens would be nice, perhaps a minimum increase in battery life for the 5G's, (ever optimistic of better!)