Random minimization in Windows.
So this has been going on for probably 6 months at least but I've never bothered to ask about it. Whatever window I'm in will randomly minimize. It doesn't seem to matter if I'm gaming or just browsing the web. Just once every hour or so, it will just minimize whatever my active window is. The one exception is if I'm watching something in netflix full screen, instead of minimizing it will just drop me out of fullscreen mode (annoying if I'm cooking or something and don't notice and my computer locks because netflix isn't fullscreened anymore.)
I have a friend having the exact same problem as well.
We're both running Win 7x64, but that's about the only real commonality as far as setup.
If it's something that's happening to both you and a friend, I'd start looking at the software both of you use, and killing them off one at a time to see which one is the culprit. It's also possible that you two have some sort of malware infection that's causing this. You might want to run the usual malware scanners to see if they find anything.
In the meantime, try running any of your problem games in full screen windowed mode, since that will keep the programs from getting backgrounded when they lose focus.
I say 'and' because the only way I've had it not minimize is to have both of them shut down. Don't what is going on that's causing them to be that way, but the mystery seems to be solved.