A nice concept you might want to try…
With Roman and Thomas we got two dungeon masters that started working on a greater plan, the three of us decided to start a few simultaneous story-lines interwoven with each other, some characters knowing a few from the other group, maybe interchanging them from time to time. 
(Though they are all played by very much the same players) We’re trying to create a dense setting and put as much information of the world over to all players involved. (Meanwhile I’ve  the honor to dungeon-master another part of the whole and I guess at least Andrea will try her best, as well, so we got everyone involved to get the maximum out of our setting). But let me tell you a little of our experience so far, what pros and cons I did experience with my two characters in this, I could learn quite a bit in a few sessions to improve as player and dm alike. Let’s hope you like the idea since I really enjoyed it that far.
When it comes to character creation I’m always facing severe problems to make decisions in this regard, you might know that yourself, first I favor wizards over everything else, secondly I have a very strong affection to complex concepts that are either capable of leadership or influence the course of an adventure. For me it is important to have a strong background on characters and I really love to interweave my story with those of other players. (I tend not to keep any information from fellow players doing so).
With our new concept of multiple-concepts we experience a few upsides and downsides. The main advantage is you can contribute a lot to the storyline with your characters and don’t have to focus on one plotline. While this is very positive – I would say the strongest and best factor is the players get to play different roles. Something usually only dungeon masters do for a longer time period. They get to get different perspectives onto the same plotline and see that actions may influence the world they are in.
The main downside of this project so far is the fluctuation is also causing troubles with the main-storylines since motivated characters for one plotline are substituted during the game and together with (our) basic player fluctuation this has caused some concern and problems of late. Secondly it is more of a challenge to seperate in-game knowledge and out-game knowledge from player to their characters.
Quick-Fazit: We’ve enjoyed this game so far, while we’re rather new at this approach, it is some fresh wind and obviously gets some players closer to playing Dungeon Master (hey, we’ve a few “applications in line” for DM’ing a few sessions). Together with the hot-seat DM this is a constant fun-providing factor for the gaming group at the moment, and I’ really happy the way it works out.
Good going for 9 sessions with shared GM-ing!
Though not exactly the same in implementation, we’ve had a similar issue in trying to avoid too heavy a load on, or commitment by, a single GM. As a result we’ve gone the other way, I think, in having a really light framework into which the individual DMs can drop their hooks as they want (and let them be taken up, or not, by anyone else).
We’ve listed the framework on the front page at http://www.obsidianportal.com/campaign/ads-greater-sea if you’re interested…
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Hi Halfbat,
sounds like a nice framework and good approach especially when it comes to rl-“problems”.
What are your experiences with Obsidian Portal, have you tried other platforms and is there a reason you picked OD for the campaign?
TheLemmings last blog post.. – Latizan and Zord – one world and a lot of adventures