I bought my iMac 24" 3.06 8800GS from the Apple On-line store in December 2008. All went well on install without me noticing any pixel issues until I installed COD4 and on the introduction black screen sighted 2 great big white dead pixels towards the bottom of the screen.
I logged out of COD 4 and went through each of the desktop backgrounds scanning the screen intently with the various colour schemes.
I found I had 5 pixels in total out. Including a bright red one (the worst of the lot as it was on eye line level).
I tried the download programs of flashing lights which you can place over the dud pixels and read up for literally hours on the internet about pixels whilst I grew depressed and angry.
When I rang Apple two days later well within 14 days of arrival (after a restless sleep weekend) I was polite and calm and explained the situation. Apple noted it all down and agreed without issue to replace my iMac. (all this done via UPS, and TNT efficiently, I just had to pack it up and label it up).
I was obviously very worried when the new one arrived but all seemed well although I must confess there
is a tiny tiny black spec of a dud pixel top left area which I located some few weeks later but I am happy enough that it is so small and out of viewing area that I can genuinely live without bothering about it because it is so easy to miss.
So, in conclusion, my experience was that Apple were very good about the exchange. I think it helps to purchase from an Apple Store or from their on-line store because you could be at the mercy of other outlets.
As an aside, I have NEVER met anyone who has "massaged a pixel back into life" and would never recommend removing glass screens and poking pens at pixels unless someone can say otherwise.
Sincere good luck.
