Well, after 1 year of screen blinks (3 months from when it started blinking almost nonstop), 2 months of repairs (1 logic board and display assembly replacement, and another logic board and thermal assembly replacement) I now have a brand new 2011 i7 MBP.
After I called Applecare back and told them that the problem was persisting even after sending it into the repair depot, they offered a replacement, no questions asked. I didn't even have to suggest it. For whatever reason, I couldn't just swap the computers out at one of my two local Apple stores, so they sent it all the way from Shanghai (via 2nd day air, no less... must have cost them a fortune!).
Overall, I'm very pleased that we were able to come to a solution that solves the problem for me. My advice to anyone else who is experiencing this problem and who still has Applecare: keep sending it in for repairs. We all know the repairs won't fix it, but keep sending it in until they agree to replace the MacBook for you. It's a hassle, takes a lot of time on the phone, a fair amount of time without your computer, and you may have to prod them in the right direction, but be persistent. And most importantly, do it all well before your Applecare is up so you're not stuck with a defective computer.
I'm still rather perplexed as to -why- the problem keeps happening, though. The repairs made it better for me (it was only blinking a few times every day, versus almost nonstop before the repair), but it clearly wasn't a complete fix and it seems to get much worse over time. I really wish we could know for sure what's causing it... but I'm guessing it's NVIDIA's fault, given their track record.
Best of luck to everyone else out there...