Yeah better performance and a better (or at least no worse) battery life would be great even if it meant a 'slight' increase in thickness.
Secondary upgrade for me would be a slightly better camera.
32gb would be simply great though.
Would also like to be able to synch wirelessly (not sure if that is hardware or software related though).
Syncing wirelessly is one I missed, though I doubt it'll happen as what would you sync? Wireless music transfer would be painfully slow so is probably out, syncing contacts, calendar etc tread on mobileme a little too much.