Twitter for iPhone and Android have been updated with some new features (as well as the new Twitter bird).
Expanded tweets adds several new partners as media sources to the app just like on web. This allows you to expand more tweets on the apps to get more content. For example tweets from sites such as Vimeo and Etsy will expand to show videos or images.
Events can now be discovered in the new app, events such as twitter.com/#NASCAR on your iPhone.
Search has seen some major improvements so you will receive more suggestions when searching people by both real name and @usernames.
Notifications has also been improved. You can now get notifications from people you follow when they send a tweet or retweet. This really helps you keep on top of particular users.