On my fourth one lol. The first had smudges under the screen the second one locked up to the point I could bot switch it back on without a soft rest and the third had dead pixels. All from O2 shop in the UK. On the third exchange they got really angry with me and refused to exchange and said there was an acceptable dead pixel limit... I had to ring customer service who I turn rang Apple on my behalf. They confirmed the store was lying and there was no limit and if I had issues Apple would exchange it for me or I could do it in the shop. I decided to try the shop again as I did not want a refurb. I had to speak to customer service in the shop who then told them they had to exchange it. Teach me for going in on Friday 13th lol. Touch wood this one is fine, top marks to O2 phone service and Apple. Btw all of them had yellow camera issue and each one was a different week. The current one is not so severe I the yellowing, it is clearly a software issue, hope Apple fix it. Guess I am just unlucky, how many have you guys had?