I can think of a couple of things that would be very nice little additions, at least on the iphone edition.
1) if I have a chat window open with a person, don't beep on every incoming message. Maybe have a 15-30 second "mute" so that if we're conversing I don't have this constant barrage of beeping/vibrating.
2) XMLRPC/SOAP/?? logging interface. I log all my conversations with my desktop client, but I have no logs on the iphone conversations. I'm not suggesting that you store them on the iphone, but since Palringo is proxying everything through their servers anyway, give me some kind of MACHINE-USABLE interface to retrieve logs of my conversations. I can write the other end (to pull the logs and incorporate them with my own), but I need something to pull them from. You don't have to store them forever, either... just keep the last 7 days of logs or something. Text compresses very well and takes up very little space, even uncompressed.
3) (on the iphone) keep the last few chat messages... if I accidentally close out the conversation window when someone just sent me something, I lose it. This would tie in very nicely with #2 above.
4) Sort my contacts for me! Pending messages, Online, Away, Extended Away, DND, Alphabetic.