I think it would be a great idea to integrate push notifications on the iPhone app so you have the option of receiving a notification immediately when someone writes a comment, and so that plugin writers can integrate notifications into their plugins as well. So if I have the Sociable plugin, for example, if someone dugg my post or shared it on facebook, I could optionally get a notification. Similarly, if I WP-Polls plugin I could get a notification if someone voted on a poll.
Also, I just wanted to mention, I have had a recurring bug on my iPhone WordPress app where the save button disappears and I have no way of saving it. After I finished the post it is gone and everything is lost.