FWIW, I do not think this issue has anything to do with sleep. In fact, I'm pretty/basically sure that I've seen the black flash after turning the computer on, and BEFORE ever sleeping it. This thing is so random, that if you've only seen it after sleeping (for example, I only turn off my computer once a week, sleeping every night instead, so most of the time, it's "after sleeping"), you might think it only happens after sleep, but I don't think that's the case.
I am also confused as to why some people say that logic board, or even display, replacements make this problem go away, since it is clearly happening with new machines. What, do they install a different logic board for a replacement than they're putting in new machines? I seriously doubt it. Same with displays.
Also, at least for me, this problem did not happen within the first few months of having the computer. It started after a while. And some people are reporting that they've never noticed it until installing 10.6. So, I have to wonder if those people with new displays or logic boards might not have (or see--let's remember, it happens in the blink of an eye, so it's easy to miss if you turn your head, or, well, blink) the problem until a couple months go by.
If only Apple would acknowledge this problem, even internally, and find what's causing it, and, of course, find a fix for it. It's such a frustrating little bugger.