The only common theme is that users are running Apple iOS 6.0.x. While impossible to discern the root cause of the home button fail, one might speculate that this is an issue in iOS as it relates to capturing the button-press event and how the OS handles that event (i.e. to which program(s) do I communicate/raise that event).
This could be pretty darn embarrassing for the iOS team, if it turns out NOT to be a hardware issue and this bug made it into the iOS release build. Just saying