A cursory look of the app shows no major changes to the UI, but the big new feature is the ability to receive Direct Messages and Mentions as pushed "toast" notifications (those at the top of the screen) and Home (live tile) notifications, which gives you a counter of how many new Tweets have happened since your last check in. (Also, search now works as well).
Overall it seems to be working very well--it's quick to push the messages/alerts and we're quite pleased. Along with GoVoice (Google) and everything is coming along nicely on WP7 just one month out. Of course the app is still free and you can download it here (opens your Zune desktop).