Well, I used to live in Seattle, and I know there's one fish stand at the Pike Place Market where the guys did throw fish around (from one worker to another, not at the customers!) and generally clown around and have fun while they work. I've seen them on feature TV shows, so it wouldn't surprise me if they've made a career out of it. I'm sure some of the 'Catters who still live in Seattle (mousethief, Don Firth, etc.) can give you more up-to-date info. But yes, I've seen it.

Aloha,
Mark