That lucky man Kevin Rose got access to try out the beta of TweetDeck for iPhone early. From his comments, it sounds good, the feature list (below) backs that up. So look out Tweetie, looks like many people will be leaving you for TweetDeck.
Personally I use TweetDeck as my desktop twitter client of choice, so to have a seemless desktop / mobile experience is definitely advantageous.
The app has been submitted and available in the App Store for free, just as soon as Apple approves it. Hurry up Apple !!
Feature List
More @ TweetDeck + KevinRose.com via Gizmodo