Since the three x86/x64 Arch PCs around my apartment are running XBMC 12.3, I decided to take a crack at updating the xbmc-rbp ARM package to install 12.3 instead of 12.2. It seems to have worked the first time, but I'm recompiling a second time on the pi after making one minor fix. I won't know how well it works until tomorrow, since I haven't figured out that cross compiling thing yet, but here's the update:
https://github.com/Romzetron/PKGBUILDs/tree/master/alarm/xbmc-rbp
Just got into using git a couple months ago, and this is my first time working with github. I was a little hesitant to fire off a pull request without a little feedback first.