"Jumping the Shark"

I recently heard some folks on the local sports radio station using the term "jumping the shark". I had no idea what they were talking about until I ran across this Slate article pointing me to (what else) www.jumptheshark.com. The premise is that there's some way to tell when a TV series is "over" -- for example, when the show introduces a new kid, when two characters whose romantic tension had driven the show end up getting together. The canonical example is Happy Days, where an episode featured Fonzie jumping a shark on water skis.

This reminds me of a Saturday Night Live ad parody I saw several years ago featuring songs that marked a similar turning point for bands...when they're no longer cool, but have descended into self-parody.