i have played in these types of campaigns before- they usually started off pretty good but quickly degenerated. the following points will help you stear clear of the issues that caused the destruction.
1) make sure the DM's set ground rules for the campaign- this will help continuity and will also help with what grimwell brought up about favoritism and differing campaign styles. if all the DM's know what the ground rules are, it is a bit easier to keep it all together. they also need to have a clear idea of the campaign goal- is it a string of modules, one of the pregenerated Adventure Paths (this would work the best for rotating GM's), are the adventured not related whatsoever (episodic), etc. are weo only playing to level 10 or 15 or we planning on going EPIC?? lots of things to be hammered out before the players even think about making their characters.
2) the DM's need to decide beforehand WHEN they will swap- is it level based, is it module based, time based, whatever- but it needs to be figured out before they start the campaign. and once you get to that point, the DM's who are to swap need to have some time to get their part ready to go- they can/should be working on it while they are playing (of course) but they might need some time to modify things depending on how the last part ended.
3) each DM runs the campaing until their part is complete- Bob finishes his bit and Larry is to take over, by that time the characters NEED to be done with Bobs bit and ready to start Larrys. if for some reason Bob wasnt able to get the characters to the next point as determined by #2 above, then Larry has extra work to do before he can even start his bit- and it might even derail what he had planned. if, for example, he has to finish Bobs bit and one of the characters that he was going to have some main plot threads for in the next bit dies and does not get raised, his part goes up in smoke before he even gets started.
4) METAGAMING- as the DM's have to have some background info on where the campaign is going, it is better to have the DM's run the same pc(s) when they are not DMing. and that PC should not ever be a central character to the plot of any of the DM's parts- play them more like a NPC that hangs with the party. this may not be as fun for that DM/Player when he is not behind the screen, but i see it as neccesary. its okay to use the DM character to keep the campaign on track but NOT okay for him to railroad the campaign towards the goal the DM/Player has in mind for later when he is behind the screen again.
there are a bunch of smaller things that can make this idea successful, but there were the main points that killed the campaign that i was in that tried this very idea. YMMV.......
no hope = no fear
dont mistake lack of talent for genius