I installed Twitterfon on this iPhone tonight. I have been using Tweetie to monitor the Twitter stream.
Twitterfon incorporates a similar feature set and functionality as Tweetie. Twitterfon does feature an autofresh and an autoscroll to the previous update. They are handy.
Yet I still prefer Tweetie. It features an interface similar to the iChat app on the Mac as well as the Text (SMS) aapp on the iPhone. It is purely a visual thing. One other thing, embedded links in Tweetie are active and can be forwarded to other sources.
The initial image displays Twitterfon and the second Tweetie.