The update features much smoother scrolling, larger tweet capacity, the ability to save pictures to the camera roll before uploading them to TwitPic, and secure HTTPS server communication. It also squashes a large number of bugs. A full accounting of the changes is available on Twitterrific's app store page and on the Iconfactory's website.
Twitterrific is still available in two flavors. Twitterrific (the free version) periodically shows ads via The Deck, similar to its free counterpart for the desktop. Twitterrific Premium is $9.99, and omits the advertising.