Labor Intensive

The following announcement from Zebraboy was posted to NPL-Folk on Aug 7, 2006:

LABOR INTENSIVE Greetings! At 12:00 noon EST, Monday September 4th, I'll be posting a 12-puzzle 'ganza online at http://www.markhalpin.com/laborintensive.html. The timing might give you a clue to the theme. There's a (modest) prize for the first person to solve everything. Hope many of you play!