Updated to 10.6.7 last night (Central Europe), and worked fine for hours (as it sometimes did before), and then today, up until just now (noon): flickering and blackouts just as before, on a 24 inch ACD that worked fine with MBP's prior to Early 2011 MBP's.
Edit: I did reset PRAM after the update and before hooking the laptop up to my 24 inch ACD
Edit 2: I notice this other very strange behaviour, ONLY on days when I've been having these glitches and blackouts. In Safari (5.0.4), when I'm on a website, and click on the bookmarks icon, and whatever is highlighted in the navigation column of bookmarks doesn't have anything in it, so that the cover flow section is supposed to be empty, this "empty" field does not refresh into the black it's supposed to be, but stays on the website as it is. Anyone else have this when they try?
At first after updating, I wasn't able to duplicate the problem, and now, just when glitches and blackouts started again, I'm easily able to duplicate it. See here:
http://img3.imageshack.us/img3/2893/safariproblem.png