I had a few issues with an original iPhone5 purchased within first 2 weeks of release.
First off, straight out of the box it had obvious scratches along the bezel (which apparently many people experienced.) More importantly, I had a a weird issue where white boxes would appear at the top of the screen (near notification center) and the phone subsequently would become unresponsive/laggy. After numerous fresh restore etc, I was luckily guided to an apple support thread of others with the same exact problem and supposedly it was due to a loose cable. ATM I felt relieved it wasn't hardware related.
https://discussions.apple.com/thread/4361737?start=0&tstart=0
So, I went to Apple but because I couldn't replicate the issue on command, they said bring it back if it happened again. I left it at that.
About a year went by before the problem became unbearable. I went back to the Apple store, and again...I couldn't replicate the issue. However, this time I recorded the problem with another device and informed them of the above thread. They told me that I was outside of my warranty (by a week) but the Genius Bar guys would open it up and take a look if the connections are loose. Ten minutes later he came back and said they couldn't replicate the issue & everything seemed fine inside.
Reluctantly, I started to leave and while examining/squeezing the phone....BAM, the white boxes appear. I immediately turned around and showed the same employee. He confirmed the issue but because I was a week over the warranty period, he said that all he could do was record the problem in the system and I could order/buy a new screen replacement for $150. At this point, while the guy is talking, I realized manipulating/squeezing the screen at the top would cause the white boxes to appear. In my mind, this only helped prove that their must be some type of a loose connection inside. The guy repeated there was nothing else he could do because when I first brought it back, the guy who originally said to bring it back never officially made a report in the system. Needless to say, I stormed out of there ready to throw the phone at the wall.
Long story short, I've since gave the phone to a family member but beforehand, I did a lot of squeezing and twisting motions near the top of the phone. Almost 6 months later and she said the problem hasn't happened again since. TBH, I doubt the Genius Bar guys ever opened it up to check for loose connections.
So bottom line, ....although I love Apple products (I currently own an iPad3, iPad mini2, (2) iPhone 5's, iPhone 4, & iPods etc.), this entire experience left a horrible taste in my mouth.