I've noticed that the themes posted here have working friends backgrounds that work with a non-JTAG xbox. Some of the same exact themes posted at Xbox 360 Premium Themes don't seem to have working friends backgrounds, unless you have a JTAG xbox. I'm not sure why the ones here work, but those others don't. They seem to have a few more themes that you all don't have posted here. I was wondering if anyone knew how to fix these so that the friends background will work on a non-JTAG xbox. Also, didn't see this free premium listed here, so I figured I'd mention it if some people didn't know.
All the themes here are free on Xbox Live so are not console / profile locked meaning they have not been modified to work on any Xbox 360. As the themes have not been modified in any way the premium features work without a jtag console. The themes at the website you linked to have been re created, basically the backgrounds extracted out of console locked premium themes and dumped in a standard theme. Standard themes work on any console, however carn't customize the friends backgrounds. Ill try the Forza theme you link to and see if it works on another console, if it does that can be uploaded here.