I love the app so far and I use it as my primary client but I've held onto TweetCaster and Twidroid, as well, for a few reasons (no particular order).
I would love to be able to access My Profile from the menu to edit my info as well as add/remove users.
I would also like to be able to search for Nearby Tweets, based on GPS location (and perhaps set a distance option in miles...5,10,20,50).
I would also like the ability to create/delete lists as well as add/remove users to said lists.
I would also like to have a built-in image viewer for twitpic, tweetphoto, etc.
Also, an unread tweet counter (just a small bubble) overlaying the timeline, mentions, DMs, etc.