There are some reports of people returning many iMacs to get a good one. But the odds of that happening have to be extremely small. Any returned Mac must be refurbished and cannot be sold as new. It's a major drain on profits. Ignoring that people with problems are most likely to post, this thread would imply that 10% of customers have a problem and that 10% of the units are therefore bad. But if that were their return rate they would certainly shut down production!
I'd say that people like Jamooche either have standards that are much higher than average (in which case they probably would be better served with a Mac Pro and a professional grade monitor) or are very unlucky. If there is a 10% failure rate, then returning 5 consecutive iMacs and finding all those in a store (lets say five more) defective would be one chance in 10,000,000,000. To have a 50:50 chance of getting 10 defective monitors in a row would require that 93% of iMacs had bad displays. Now indeed to a critical eye this would be the case -- the design of the monitor with just "white" LEDs for backlights and temperature gradients will keep them from being acceptable, but if most people found them unacceptable then they would have to cancel the product line! The bottom line is that most people find them more than acceptable.
Very good point. I've never had this problems on any on the Macs I've owned nor at the uni I used to work for. I believe some people have a more enhanced level of visual acuity and are able to discern faults not apparent to the general public. This people are very hard to please because they are more sensitive to any visible (to them) defects.
Cheers,