Probably the most welcome change in the new UI, however, is what Google is calling the Action Bar. In every application, the top bar is reserved for contextual options, navigation, or other buttons. The Email app, for example, has a new message button and a refresh button at the top. When you select a message, that action bar changes to display a move to folder button, a mark as read button, a star message button, and a delete button. Of course, it also has dropdown menus for any buttons that overflow off to the side.
Why is this so awesome? These are the kinds of buttons that, on the 2.0 cycle of Android, are usually buried in menus that you access with your phones Menu button. Now, instead of having to hit Menu (and God forbid a "More" button), those options will be available right at the top of your screen. Really, this is one of my biggest complaints about Android, and it makes me wonder why we don't have this action bar in 2.x, too.