I was over at Redbears Ravings Blog, and he was waxing lyrical about a Campaign he had a hand in running many Moons ago - with two DM's and a veritable Horde of PC's.
It sounded amazing, check his writeup here - REDBEARDS RAVINGS
The COOLEST thing I ever did (IMHO LoL), was to run two Parties AGAINST each other. I had two groups, one that consisted of players of - well lets say 'unsavoury' Alignments, and another of 'Goody Two Shoes' Characters.
To begin with neithe group knew about each other, and were constantly foiling each other plans annonymously - then as the Campaign progressed things stepped up a notch including the Bad Guys infiltrating the Good Guys Group (till her Alignment got revealed and the Good Guys put her in Jail and out of the Campaign - BOY she was p***ed Lol).
It ended with a BIG confrontation, luckily the Good Guys won or it could have Royally Screwed my Game World!