Here is a history of my returns.
#1 - Dust between glass and screen
#2 - Rattling/loose sleep button
#3 - Proximity sensor issues on nearly every call
#4 - Dead pixel
#5 - Dead pixel again
#6 - Proximity sensor again, though not as bad
#7 - Dust between the glass and screen again
The 8th phone turned out to be pretty good. No proximity issues yet,.. No dead pixels, no dust on the screen.. I have recently noticed a tiny spec of dust under the lens of the camera though. I figured I was being a bit ridiculous to return it at this point. It still shoots amazing photos. I looked at my 3GS to find a long piece of dust floating behind the lens. I then looked at my point and shoot digital and noticed a LOT of dust. The fact is,.. the longer I own and use the phone, the higher probability of dust accumulating in there. Its not affecting my photos so its nearly pointless to waste time try to exchange it for some other factory imperfection.
Point is,.. if you dont like your purchase, use the available means to find one you do like. Apple has put into place a system that allows us to have a near perfect product. The frustrating part is receiving products with flaws and trying to convince ourselves that its "ok" to have purchased something that doesn't live up to our expectations. I really like the iPhone 4 but I didn't want a phone that wasn't what was advertised. I want to be satisfied with my product or I do not want to pay for it. And with the ability to return the phone, I dont have to pay for it until I am happy with it. Just remember, with their system in play, its easy to get REALLY "nitpicky." Everything you've ever bought has had some factory installed imperfection. The main reason we're so crazy about getting it perfect is because of forums like this that make us aware of what to look for. Remember, ignorance is blisssss..
and
Nothing is perfect..