Porting apps from iPhone to iPad isn't just resizing all your assets, your app needs to be re-adjusted to use the larger space and how your fingers don't cover up 1/5 of the screen when in use. TweetDeck does this.
The landscape view looks like it does on the desktop, giving you multiple columns for a Command & Conquer General's-eye-view of tweets going down. Great for keeping track of who you follow, Tweets directed to you, multiple searches and DMs all without having to tab back and forth between screens.
It's still useful in portrait, trading one column for a big info panel on top for individual tweets/people. Best of all, TweetDeck is free. Freeeeeeeeeeeeee. [iTunes]