For those waiting on a week 50 machine, I'm happy to report that my week 50 i7, received Friday, is tip top. No flickering, no yellowing, no loud HD (came with a 2TB Hitachi, and I did not reinstall OSX), no dead pixels. I did have an issue with the keyboard and mouse being recognized immediately following a reboot but they eventually connected and it may have been a one-off occurrence. It's enormous, quiet, beautiful, and fast.
Update: My screen does in fact have the yellowing issue. It doesn't bother me, but it doesn't bother me enough to consider a return (unless it gets worse). If I hadn't taken the test, I wouldn't have realized it. Still satisfied, but YMMV.