The test theme that we recently put out for testing has been retired as it seemed to have too many issues. We'll continue to work on new ideas for the forum, but for the time being we're forcing everyone back to the default UsingEnglish.com design.
Don't worry, I'll be trying to test out new themes again very soon, but there were various people suggesting that that version caused problems with using the forum. I think I need to do some more testing on it before releasing it again.
Additionally we have to upgrade the forum software (vBulletin) and that will require using a brand new theme built from scratch. I therefore want to consolidate my efforts a bit.