I\'m running Eclipse Helios on Mac and just updated to ADT 9.0.0.
It seems to have broken the Layout editor.
Any time I try to open a layout xml file with the layout editor
I just stumbled across this same issue now. There seems to be a new dropdown in the "config" section for selecting a platform version (none was selected in my case). Selecting any (eg. "Android 2.2") made the Theme selector appear, and the layout works agin.