At this point, after the Maps fiasco, and all the case issues, you could almost make the argument that people are just picking on the iPhone 5 out of spite; it sometimes feels that way, at least, but the fact is this is a hugely high-profile smartphone launch, and Apple should have expected its latest product being put under the magnifying glass. The latest problem to come to light affects the phone's on-screen keyboard, displaying some odd video corruption when in use.
As you can see in the video below, the problem manifests itself as a series of horizontal lines, flashing with varying levels of brightness in an effect that's reminding some of analog display static. The regular spacing of the bright spots has us thinking that this is a software issue, where either the wrong spot in RAM's being accessed or unintentionally written to.
Reportedly, this anomaly only occurs during certain uses of the keyboard, specifically when you're entering-in passwords for your Apple account. It doesn't seem to impact functionality any, but just looks a bit ugly and speaks to a lapse in quality control. Look for Apple to tackle this bug in a forthcoming iOS update.