Biggest problem with Big Picture Mode? How do you just exit out of Steam? If you go to exit, it puts Steam back into normal mode. I would be using it alongside XBMC, so I need to be able to swap between them.
Also, the HD4000 in my i3-3225 could use a bit of Blast Processing™, because it cannot handle Sonic Generations at 1080p at low detail. Although, I wonder if that's a fault of the game? I went to play it on my desktop (GTX 680), and with 3D on, the game definitely had some framerate drops at 1080p max settings. It was mostly during 3D Sonic with crazy stuff going on around me. You just wouldn't expect to need a GTX 680 for Sonic.