Just to add my own experience with this GPU freeze issue.
I brought my MBP yesterday at the genius bar for 2 problems: a nasty white spot on the screen (called "mura spot") and these random crashes with Yosemite.
The genius decided right away to change the screen as the laptop is still under warranty (kudos for that), but the graphics problem left him wondering.
He asked other colleagues about the symptoms I told about it(occurs when switching from integrated to dedicated, more often in yosemite than mavericks, reducing transparency and removing flash helps, etc ...), but nothing led him to the conclusion that the issue was hardware related.
The genius was reluctant to change the logic board, and offered me to test the machine for some time and have a first hand experience on the crash.
So, my guess is that Apple isn't addressing the problem at all; aren't they even aware that many rMBP users are affected ? I will get my macbook back in a few days, so I'll keep you guys posted. To be honest, I'm pretty sure they won't solve the issue, but who knows ...
Keep faith !