Swipe to Reply. Swipe over a tweet in a list to bring up a shortcut menu.

Mark All as Read. Double tap on the messages icon to mark all of your DMs as "read".

Swipe to "Go Home". Sometimes you may be drilled down very deep in a navigation stack. As a shortcut, you can swipe over the Back button to go back to the main screen.

Multi-follow. If you have multiple accounts, you can follow and unfollow a person from multiple accounts simultaneously.

Link to Address Book. You can link a Twitter contact to a contact in your Address Book. Once linked, you can associate notes, email addresses and more. All of that information will be backed up when you sync your phone - even if you delete and re-install Tweetie.