[nitroboost]

2014/04/14: Some users noted, that after upgrade from saucy to trusty there was a 100% load on home screen. If that happens to you, please start from a fresh profile by e.g. removing your .xbmc directory.

There may be multiple causes (and I guess if an .xbmc wipe fixes it, it might not be this), but when I initially upgraded I didn't do the ppa purge prior, and the upgrade had some package conflicts. I was seeing 100% load on the home screen after booting into trusty, which was caused by software processing, the proper drivers weren't being loaded for full acceleration (didn't check the Xorg logs, but guessing it was using the generic vesa driver?). Anyway, I purged the ppas and that rolled back packages, but some of the packages that failed to install during the initial upgrade were still missing. These were the ones I had to do by hand, in case it would help anyone else:

sudo apt-get install libglamor0 xserver-xorg-video-glamoregl xserver-xorg-video-radeon xserver-xorg-video-all xserver-xorg-video-ati

After that I had XBMC running like a boss again. Otherwise an easy upgrade!