Craig, thats just it. Im not saying its simple at all. Personally, I find it a massive inconvenience (not to mention highly disappointing) that my brand new iMac is likely faulty, as confirmed by Apple themselves. I wish very much that a software patch would fix it instead, as it would be much less hassle, and i'd be prepared to ride the problems out a bit longer until such a patch is made available.
However, i've installed 2 patches now, and the fault is still very much there, which doesn't bode well.
If you take a look on the Apple discussion forums, you'll find not only many very similar reports there (i've posted there too btw), but also reports from people saying that almost identical issues happen on their new iMacs when booted into windows.
So the fact it happens in 2 entirely different operating systems would suggest a hardware fault too. It could of course still be shoddy graphics drivers in OS X and XP of course, but by this point its starting to look rather more unlikely.
As for AppleCare staff not being allowed to confirm bugs and whatnot.. If that is true, then its absolutely ridiculous.
If you would prefer to wait before returning yours, then by all means do so. But I still think that if your iMac shows these symptoms, then its a good idea to at least log the problem with Apple.
The longer people leave it unreported, then the less pressure Apple have to get on with fixing the problems (be it hardware or software). Leave it too long, and you also lose option to get a refund or exchange. I say, the sooner its reported, the better it is for everyone affected.