Apparently themes still work! After a fashion.
http://www.mirick.se/aaaab.jpg
It's still possible to activate themes by going to Community -> Theme Blender -> click on "CB2" to the right of any theme. Problem is, you can't turn them off..
So I guess this is both a bug report and a plea for help because oh my goodness my CB looks horrible. :(
I tried clearing all private data in Firefox (cache, cookies, everything), tried logging in with IE, no dice.