An update.
Upgraded my OpenElec box to 13.1 and have to say that things are still very weird. Tried all of the available themes, incl. the new ones that weren't packaged with OE when this thread started.
Still, none of them really feel comfortable when using a remote control, only (no mouse, no keyboard, no touch).
The biggest annoyance to me is that in all themes, when using a remote control it's never clear how to enter a submenu level or how to leave to get the parent level. In every menu, it's different.
There is no rule. Sometimes you enter a submenu by pressing "OK", sometimes with an arrow button. Sometimes you leave to the parent level by pressing "back", sometimes an arrow button. For examples, see first posts in this thread. Examples from Confluence: Entering a submenu level from the Main menu is different than entering a submenu level in the Settings submenu is different than entering a submenu level in an Addon configuration menu. This is madness.
IMHO, most themes are far too small in a 10ft ui situation. When watching TV, I'm sitting in a living room quite far away from the screen, yet most themes are using small fonts and there is no setting to increase their size ("zoom" doesn't help here, I only want to increase the font size and reduce the number of list items accordingly).
Allow me to point to a previous post which suggested
three humble rules for a good 10ft ui.
Disclaimer: This wasn't meant as a flame. My box used to run Linux vdr, I switched to XBMC to enjoy its superiour media playback. vdr's user interface is simple, all menus behave exactly the same. So simple that you never ever get lost in its menu structure.