A little while ago, there was a zombie gathering at Monroeville Mall, filming site of George Romero's classic Dawn of the Dead. That's surely the most appropriate place that such a gathering has ever taken place, and it was a two-day festival to boot.
Mokalus of Borg
PS - Too bad there's only one picture in the article.
PPS - And that's in black and white.
Update: More news here. Also, apparently this was the largest zombie gathering to date in the world: 1124 people.