Any http request to any wordpress.org web page or file (.zip .gz , etc !) with 'themes' in the url is redirecting to http://wordpress.org/extend/themes/.
So theme updates and downloads are failing. Obviously, so is browsing the themes directory.
I sent an email to Matt, since trying to post about an issue with 'themes' was futile. (See 'illicious' post...or, rather, you can't see it right now, right?: http://wordpress.org/support/topic/site-navigation-for-themes?replies=1)
(Then I figured out to add a space in 'theme s'. Hope this works...)