Personally - Never had that happened to me. Shooting wise - it has happened a couple of times when I find a model I thought was top knotch from her previous performances.
I've met plenty of girls that I'd been gawking at online for years and when I met them, they were just as good in person. These are girls I admired BEFORE I shot them which excludes some of my personal favs (Victoria, Natalia, etc.):
Ebony: Cool as hell and fun to be around. Flawless in person.
Babe Wonder aka Fury Khan: beautiful in person. Seductive. Very cool once you get past the guard.
Jayla: Cool, mild-mannered, banging body.
Foxxy: My eyes hurt when I met her. Not a flaw on her. Gorgeous.
Logan: Very down to earth, sexy, huge booty.
Neon aka Brownie: One of the most passable girls I've ever met. Very cool, laidback personality.
Star: Very sexy, hilarious too. She always makes me crack up.
Asia: Very good looking, good to hang around.