We're starting to hear a few reports of the dreaded yellow spots disappearing from the iPhone 4's display after a day or so of use. Interestingly, someone posting on the AppleInsider forums seems to know why:
Apple is using a bonding agent called Organofunctional Silane Z-6011 to bond the layers of glass. Apparently, Apple (or more likely Foxconn) is shipping these products so quickly that the evaporation process is not complete. However, after one or two days of use, especially with the screen on, will complete the evaporation process and the yellow "blotches" will disappear. How do I know? I was involved in pitching Z-6011 to Apple.
If this can be trusted, it's very good news for those afflicted -- though hopefully Apple will keep to its usually painless replacement policy for defective phones either way. We are still seeing some mentions of the spots sticking around, fading in and out based on the heat of the phone, but we'll give it another day or two to really see how much of a problem is going to be. Let us know how yours fares.
[Thanks to everyone who sent this in]