I'll tell you my tale of woe.
After being a proud - and non-complaining - owner of an original iPhone and a 3G, I decided to "early adopt" and go for the 3GS.
The one I received directly from AT&T had a problem with the 3G receiver; it would display the Edge icon and no bars though my wife was standing right next to me with her 3G and she would have 3G service and full bars. I made an appointment at the local Genius Bar and luckily, the 3GS displayed this abberrant behavior while I was there so they swapped it for a new one.
Unfortunately, upon arriving home, I immediately noticed that the replacement phone had a yellowish tint that was more pronounced at the bottom. Sounds familiar, right? So I trek back to the Apple Store and was told that the screen was fine. I dragged the genius over to the display models and he finally had to admit that mine was noticeably yellow when compared with those. He agreed to swap it out. The replacement was less yellow but the tint was still apparent. On top of that, the screen was completely out of whack, jutting up above the bezel on the entire right side. He swapped it out one last time for one that had a level screen but still a distinctly yellowish hue that was, again, more pronounced at the bottom. I decided to cut my losses and settle.
On the way out, I chatted with one of the floor guys who saw that I was a bit unhappy. He listened to the whole sad story and suggested that I might have better luck at another Apple Store (I live in between two Apple Store locations). I mulled it overnight and the next morning, I decided that for $300.00, I was not going to settle for an inferior product. So, I trudged over to the second Apple Store and explained to a decidedly less-interested genius that I only wanted a phone like the two I had previously - or, at the very least, could I get one as nice as the display models.
To make a long story a bit shorter, I was never treated more rudely in my life in any kind of retail situation. I was told that they would swap out the phone one more time but that they would, under no circumstances, turn the phone on before the swap to check the screen tint, and they would only do it if I would sign my name on a document agreeing that this was the last swap. I was allowed to verify, however, that the screen was level with the bezel, etc. on the replacement but that was it. I reluctantly agreed, mostly because the "genius" was creating an embarrassment factor among the other people seated at the counter.
I got the new phone and...you guessed it...no change whatsoever. Slight yellow tint overall but more pronounced at the bottom. I've decided to keep this one - I need it for my business - but I still grouse about my experience with this product. I loved my first two phones and never had a single complaint about either. In fact, my wife has my old 3G and I am jealous of her nice white screen (that was once mine...!)
Again, to be treated like a crank when I've never even been to the Genius Bar before my 3GS purchase was very unsettling. Plus, they claim to not be aware of the problem or this thread (that now spans 50 pages!) None of this makes me warm and fuzzy about ever buying a Mac, I can tell you that. I'm just not sure what to do now except swallow hard and shut up...