Jumping The Shark

I have to admit that I never heard this expression until my bro-in-law mentioned it on Easter. Here's how the Urban Dictionary defines it:
"when your favorite show starts to flag and go downhill, as when Fonzie jumped the shark on waterskis. We all knew that Happy Days was on its way down then."
An example:
When Rudy (Cosby show) hit puberty, and they added that new little girl that was Denise's step-daughter, that show DEFINITELY jumped the shark.
I never thought about this before, but I've seen it time and again and it is normally when the show is desperate for ratings. I kind of thought Grey's Anatomy "jumped the shark" with the Izzie seeing/talking/screwing her dead boyfriend for week's on end, but when they announced she had an inoperable brain tumor, it made sense (at least in a prime time drama kind of way). I'm sure you can think of your own examples. Check out this website http://www.tvguide.com/jumptheshark for some prime examples.
And, for what it's worth, here's Fonzie jumping the shark (could they have dragged it out any longer)?