The new app features something called "Top Tweets" which lets you see what people are talking about on Twitter, even if you're not logged into the service on your phone. It also lets you view Trends, Suggested Users and Nearby tweets, all before you authenticate with Twitter.
If you do log in, you'll have access to the standard Twitter features (replies, messages, etc.)
Note: Chrome users have to install the WMV plugin. IE and Firefox have native WMV playback, however. If you're having trouble viewing, stream it from here instead.
You can see more of the Twitter app in another video posted on YouTube a few weeks prior: