Last year I had an in depth review of SimplyTweet 2.3 and later 2.5.
With the release of SimplyTweet 3 [iTunes App Store link] MotionObj has improved on a Twitter client that is already amazing. As mentioned in my review last year, many of the features in SimplyTweet 2 were later adapted in Tweetie 2, it is surprising why Twitter did not purchase SimplyTweet instead of Tweetie.