There is a new "Zoom to Fit" action in the layout editor toolbar which lets you scale the view such that the full screen width fits perfectly in the editor. This is particularly useful when designing for large screens (such as the tablet screen size added in Honeycomb).

You can now also zoom using keyboard shortcuts: "+" to zoom in, "-" to zoom out, "1" to zoom to 100%, and "0" to zoom to fit. These only apply when the layout editor has keyboard focus.

(Finally, the zoom toolbar has new icons and a slightly different order.)

Details: https://review.source.android.com/#change,20457