I recieved my second imac yesterday with the same gradient issue. This time around the person at apple seemed to have more information than last time though. First of all he said YES THERE IS A PROBLEM with the 24" screen. Although he didn´t know how widely spread it was he stated that it´s clearly an issue and didn´t hesitate to send me a new unit. According to him there are two different suppliers of the panels used in the 24" and one of these suppliers are making bad ones. He also said he found it really strange that the issue was not fixed yet and insisted to get me a replacement until I got one with a good screen. I consider this good news and hopefully apple will get this sorted out real soon!