I did hear a story a few years back about a FSDO inspector overhearing a conversation between a CFI and his student at a diner. Basically, the CFI was bragging about his low-flying exploits, and giving the student tips while telling him how much of a blast he was going to have when he got his license. The inspector tracked the guy down, and he was called in for a re-check. I can't remember the outcome, but acquaintances told me the guy was a total tool as a student, as well as after he managed to get his CFI ticket.