i have fullscreen movies playing at the same time all the time - but his point was that in order to change the mouse focus, you pretty much have to minimise both, then bring up the app second monitor, do what you wanted to do-then bring up the app on the main monitor.
multi-monitor doesnt play nice, since there is no way to get the focus off the fullscreen app on the primary monitor, WITHOUT minimising it
(media remote works well for the movies, however)
Still using age old BSPlayer for movies & stuff. All that is needed is checkmark on remember movie position and windows size/start full screen. Everything I click open runs on my TV full screen. Was even simpler when I still had both monitors hoooked up on same card. Now with different cards control panels has to stay on the 1st monitor.
Anyhow, have had the same problem as OP for years and it's hitting the power button constantly. Another thing would be to be able to select which monitor to use on games. I've seen one that had the option to select display. Not that I have gamed on my TV, but now that I have the 360 pad, it would be easy on some games.
Not that hard to change primary monitor, but as I have different resolutions I end up with tiny windows and messed up shortcuts and what not. So I just game on the monitor.
Maybe Windows 8 does some magic and would allow to enter power saving mode on any monitor you have hooked up, or even monitor independent screen saver
Mussels' first reply was spot on.