No company is perfect. It appears that there have been issues with the white iPhone 3GS overheating and discoloring easily. The rumors didn't attract very much attention at first, but reports continue to file in.
Apple hasn't taken the issue very seriously yet. They've updated their support document entry on iPhone overheating to include the 3GS, but that's as close as they've come to dealing with the actual problem. Apple states that overheating phones will show a warning screen and lock down for all non-emergency calls. This doesn't address the primary current issue; the fact that overheating iPhones are discoloring.
It's possible that the issue is due to a faulty battery cell in the iPhone itself. Wired has done an in-depth report on the subject and believes that the broken part might necessitate an iPhone recall. This would be a huge blow to Apple's already marred 3GS launch.