I'd say it's widespread. I had 3 early-09 15" uMBPs and returned all three. The first one had a busted LCD backlight (only half of the screen would light up) and the other two both had backlight flickering issues at pretty much anything other than full brightness.
My experience with those last two uMBPs leads me to believe that the flickering is a symptom of a larger issue with the power subsystem of the machine (i.e. a design flaw). I never saw the problem when the machine was plugged into AC power (although I gather that others have) and the issue was exacerbated whenever the machine was drawing more power (e.g. increased CPU use for flash ads in Safari, accessing the HDD when loading an uncached program, etc.). Happened with either of the 9400 and 9600 cards enabled.
I have been waiting for Apple to fix this problem before buying a new MBP. I was saddened to read that the updated MBPs are also exhibiting this behavior. I called AppleCare to report the issue with my second machine and they indicated at that time that the problem was known and that a firmware fix was forthcoming. That was back in ... March. 🙄
<rant>
Personally, I'd wait until we have confirmation that the issue has been fixed before going near the new MBPs. I'm very disappointed with the quality of the newer Apple notebooks (MBP flickering, MBA lines). It's not like these problems are minor issues like the SATA port running at 1.5 vs. 3.0 Gbit/s; these problems are directly affecting the usability of the machine and are, IMO, completely unacceptable.
</rant>
