I've had upfront installed and working just fine. Then suddenly, my pages that used it broke and wouldn't display at all! I'd tried creating a dummy site and doing preview on Upfront themes and they do not even preview.
http://www.humaneclectic.org/ezra is an example of a site that was working and is now broken (there was a lovely slider and all textures as well as being able to launch the Upfront editor will not load). I cannot even pick an Upfront theme without it breaking that site.