Troupe play was one of several innovations (there's that word again!) in the Ars Magica RPG, and one of my favorite tools! In AM, there are two types of character, and every player has one of each. There's the Magus/Maga - the wizard(ess) type, and the Companion - a very competent non-mage type. There are also a bunch of Grogs - peasants with skills - who can be played by anyone. The idea is that folks took turns being GM, and the rest of the players played either a Magus, a Companion, or a Grog.
I prefer my troupes a bit less codified. All the In Harm's Way military/historical series games have troupe play, but none have the rotating GM role as a centerpiece. In addition, though the Napoleonic Naval, Aces In Spades, and Aces And Angels games have a three-fold division of character types, lately I've been using a different way of setting up.
In Wild Blue, I started using a Mission Impossible Troupe. In the old TV series, each episode Mr. Phelps - Peter Graves' character - sorts through a stack of candidates and theoretically pulls out those most suited for the particular mission - though he always seemed to pick the same people. In a Mission Impossible troupe, there are a bunch of characters of various sorts, and the leader of the group chooses the composition of the party to suit the adventure at hand.
In Wild Blue, which was about Modern Mercs, he'd generally split it up by specialty - pilots together, or SpecOps types together, though there was nothing set against a mixed composition party. My newest game, On Her Majesty's Arcane Service - AKA OHMAS - uses a MI troupe too, though I haven't written that part yet. The criteria for inclusion would be much more focused on getting the right group of skills together, as the game is far from military. It would be much more like the theoretical composition of parties in the MI TV show.
I think there's a lot more potential to be mined out of developing the Troupe Play concept. Given my penchant for military games - where Troupe Play is ideal - I figure I'll be doing more of that development.