Yes, I just got my white iphone 3G replaced due to lots (not just a few specks) of dust leaking in under the glass. The genius bar guy brought out a replacement phone from the back, and claimed that it is a brand-new one, not a refurb. It still had the plastic protective film on it.
After using it for a while, I noticed that the text was not as sharp as on my original phone, purchased in September, 2008. The difference was so great that I took the phone back a few days later to see if I had gotten a defective model. The genius bar guy said that he couldn't swap the phone for me again just for a complaint about the screen quality, and that most likely, any replacement he would have given me would be exactly the same.
So I then looked at the display models in the store and noticed that every white 16GB iphone in the Apple store had the same blurry, poor contrast screen. A side-by-side comparison revealed that the black 8GB iphones in the store had a much sharper screen, but with a yellow tinge. These are clearly different LCD screens, rather than unit-to-unit variations. Tilting the black iphones vertically caused the yellowish screen to turn greenish whereas doing the same for the white iphones caused the white screen to just get dimmer without changing colors.
When viewing pictures, the white iphone screen made the pictures look washed-out, grainy, and one-dimensional. The black iphone screen revealed much more detail in the pictures and a more smooth, 3-dimensional image. I couldn't do a comparison, but I think my original white iphone had a clearer display which was much more like the current black iphone's. Too bad it is not an option to try to get one of the original ones anymore, but I guess I wouldn't want one anyway, given the poor seal/dust leak issue.
I've read that there are also screen issues with the new aluminum Macbooks with one set of screens made by LG and one set made by Chi Mei, and one of these two being much better than the other.
My new phone is not unusable, but it is disappointing that the new screen is so poor compared to the original one. It is much more like a typical cell phone screen rather than a computer-like screen.