It's five dollars. It has half the functionality of Twittelator Pro. But Birdfeed just became my default iPhone Twitter app.
It's fast. The fastest Twitter app I've seen since Twitterfon (which isn't that fast anymore, once it started inserting ads.) The user interface is even cleaner and more spare than Tweetie's—the app it will inevitably be compared to the most. For instance, the "load more" button at the bottom is gone—you just keep scrolling down, and it keeps loading new tweets.
It's the opposite: A remarkably focused and well thought out exercise in restraint. It's the details like a timestamp marking every time you open the app so you know where you left off, that shine. If you only use the core Twitter features, Birdfeed is the best app you can buy.
That's not to say it's necessarily better than TweetDeck or Twittelator. The amazing thing about Twitter is that you can do whatever you want with it, and having all of those features is fantastic if you need them. Birdhouse is simply the most essential Twitter app for iPhone yet—it's only what you really need, beautifully designed.
It's not perfect—it freezes for a second when loading new tweets, like you hit the bottom of a timeline and starts pulling in more, and then there's that account amnesia bug.