Till recently, (IMHO) Android Developers had a very bad experience in designing graphical UIs for their Android apps. Personally I never relied on the graphical designer that was provided with the Android Eclipse plugin. It just didn't do it's job well. Then later, Google launched AppInventor, a simple way for (as they claim) even non-technical people to design their Android application. It basically allows you to create your app by composing together pieces of functionality in a very interactive, graphical way. This made me wonder a bit: why did Google invest into an online - say - graphical editor for Android apps when their Eclipse based editor used by the mainstream of "serious" Android developers really sucked?? But it was clear that it was just a matter of time till they would enhance that one as well.
Now the time has come :). In the Google I/O 2011 talk below, they present their enhancements on the Google Eclipse plugin, focusing mainly on the UI designer. And it's really amazing what they did...have a look