I've spoken with several people about that glitch, and from what i've heard, none of them have been able to reliably recreate it... one of them was able to do it one time, but even repeating the same thing while standing in the same place didn't cause it to happen again...
Personally, I don't think there is a glitch in the IPhone 4, it is alot of media craze about something that no one else can recreate...
There has even been speculation that because Apple is a REALLY big company and doesn't support any body policily that the media decided to just go after them...