Caveats. Someone’s probably already beaten me to this, but:
Telecanter can DM until a quorum of players is creeped out by his creepy antics.
Roger can DM a low-level game of Vermin & Varlets.
Zak S. can play and DM but he can’t bring a film crew.
The Lord of Green Dragons can DM if he promises not to use Robilar as an NPC, and he can play if he promises not make comparisons to how Gygax would have run it.
Alexis can play if he plays nice (which means he can’t play) and he can DM but must take a shot every time he says he already thought of whatever the players say.
Pat can play if he keeps the hell away from my henchmen.
Rolang has to play a wizard on the way to lichdom.
Scottsz can play, but he cannot DM with TSR modules because he will probably TPK any party that doesn’t treat it as hallowed ground.
James Mal can DM or play but he must take a shot every time he says “Just so” or uses the word “bemused.”
JOESKY CAN PLAYS BUT HE NEEDS TWO USE HIS INSIDE VOIICE.
Chad must DM his “Black Sabbath” campaign.
Christian can play but he can’t DM that WoD crap unless he brings food.
David can play and is the only one I’d let DM 4e.
Jeff can play but he can’t DM ’cause he spoils his players.
Cyclopeatron can play the banjo, or can DM his homebrew world.
ze Bullette can play or DM or whatever the hell he wants.