Very weird... Pi signal to tv (hdmi) is perfect until XBMC interface loads (openelec). At that point the video starts glitching. When at a menu and the pi is inactive, it's fine. As soon as I step from one menu item to another, I get two "glitches" as the Pi does something and the screen goes blue momentarily. Then it settles down again. Use the arrow keys again and once more it glitches.
When I rescanned my movie library just now, it just sat there flickering blue on and off as the Pi did some processor work.
Does this on both my Model A and my model B Pi. Only in XBMC, whilst in Debian Wheezy or something it's absolutely rock solid, no glitches at all.