[alcimedes]

My machine has never used anything but the dedicated graphics card.

No matter what I'm doing, it always says "High Perf." for the Graphics card setting in activity monitor.

I've toggled the option to turn it off when on battery power, but I've never seen it work. It's like the machine is always using the high performance card.

I presume the built in card is capable of pushing video to a second screen without having to invoke the dedicated graphics card.

edit: So, started a thread over at Reddit to see what others are experiencing, and it sounds like there's a decent chance the OS Beta update will resolve the issue. I've signed up for the beta and will be installing it tonight, will update with what I find.