I've attended very few events, and most of the ones I attended weren't very good (PTU Epcot event) but ones that seemed to generate the most buzz: The first, I'd say 3 Epcot pin celebrations. One of them, had a place where they were selling pins cheap including the leftover Millennium Village CM pins. Also, the Disneyland Divas merchandise event. DL had had a couple of merchandise events in the past (Pirates, toad) but that one was after Pin Trading had really taken off and when people found these as "gifts" people went bonkers.
Also, I remember people thinking the events at Animal Kingdom (Parti Gras, Adventures in Pin Trading, Pin Route 498) were always the best managed pin events. Good boards, good gifts, good food, short lines.
Oh, and an "infamous" event. The "gift" for the 2003 Happy Haunts Event, was not a pin, but a cheap plastic red cup. The next year they revisited it by releasing a pin of the cup.
WDW, also used to hold small quarterly events. They would be used to release some LE event stuff, but also first chance to own some park things. That's where a bunch of the maps came from with spots to hold pins. The one with the most "in demand" releases now, may have been the Princess Ball pins
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