Being a co-dungeon master

Our D&D group is a pretty good size. The average is about 4-5 players, we have 7. Because of this, I felt that helping the dungeon master (@sdwrage) out would be better than playing and plus, I always wanted to be a dm someday.

Well, things worked out for about 5 sessions but we finally decided it was just more trouble having two dm's than it was for a single dm to handle such a large group. The trouble was not so much that we fought or disagreed, because that was far from the truth. In fact, together, we created a story that all of the players have really gotten into. The problem instead was caused by a lack of communication and a lack of a 'system'. 

Basically what I did was helped create the encounters and story line before the game started and during the game, I would be the 'list keeper'. I kept track of initiatives, creature hp and ongoing effects, etc and helped with looking up creature stats and rules that we were unclear about. This all sounds fun and pretty easy, however it really isn't. There are several issues which prevent it from flowing correctly which I will address here.

1. Keeping a 1:1 communcation between the dungeon masters. I would often be in the middle of updating creature stats only to find out that it wasn't zombie 1 whom just took damage, it was zombie 2 and now zombie 1 just took 13 damage, zombie 3 was knocked prone and zombie 2 has ongoing fire but zombie 1 saved... so now I have to go back, revert back to the previous values, redo the math (not difficult but your dealing with a lot of numbers) and then make sure everything was correct which sometimes was impossible without knowing what was going on while I was in the middle of updating the information. However, the primary dungeon master is busy dealing with 7 players so you can't complain really.

2. Players. While it was cool to be able to deal with several of the players my self, while the other dm dealt with the others, it also sometimes created complications. The players all figured that since there were two dm's, they were free to talk and ask questions during someone else's turn. This often leads to everyone being on a different page which of course is not good for the party.

3. Rules. I can't lie. There were times when we would definitely argue about rules. I more often stuck to the official rules where as he often would deviate. While it is fine for a dm to deviate at times, I sometimes disagreed about said times.

4. Style.  I say try to kill the players. Don't fudge rolls because the party is almost dead. They should have tried harder or made better decisions. If I'm a level 4 player and I run into a cave which I've been told is the home of an epic level dragon and I die...yeah, I deserved it completely. I'm not saying he would prevent them from dying in a case like that, and actually a character died just this past Sunday for insulting a level 18 mind flare (he was a level 6).  However, I say use all of the creatures abilities, make it seem real, like the creature is fighting for it's survival, for it's honor...for it's dinner. Don't back off just because the cleric has no heals left and the rest of the party is down. (Although I do believe in the one time reset button in the event of a TPK).

What we did do right I think:

1. Used a laptop.

2. I created a spreadsheet template which we used for initiative, xp, encounters, etc.

3. Planned out enough of the adventure to last several sessions at a time.

If you have ever played in a group with more than 1 dm or have co dm'd, please tell me how it went for you and what you did that made it work or why it didn't work.