Hmm. It seems to me that my group is weird in that we collaborate on almost everything... there's very little that rests on the say-so of only one person.
Social aspects and hosting considerations are pretty much moot for us, admittedly, since we game online. If you want to smoke up a storm, drink a case of beer, or play Metallica at top volume while RPing, nobody cares as long as you still pay attention to the game. (Though, weirdly enough, AFAIK everyone in my group happens to be a non-smoker and at least mostly a non-drinker anyway.)
Scheduling is a group activity. We're willing to work around any occasional week that a person can't make the establishied schedule. However, if someone is constantly having problems making the RP night, we usually have to let them leave or drop down to semi-NPC status, because our current schedule is already pretty much the only one that everyone in the group can make regularly.
Adding/dropping people is mostly a group activity. New additions have to be approved by everyone - although unless the person seems to be a jerk, we're usually permissive to anyone who decides we seem fun to game with. Theoretically a DM can turn away a new player if he feels there's more PCs than he can handle, but in practice we have a hard time just keeping the number of PCs at the standard four (Real Life manages to get in the way a *lot*).
The DM technically has control over what setting and campaign idea they want to run with. However, since we as a group tend to brainstorm ideas frequently, and our DMs always ask if a given story from the idea pool that they want to run with sounds fun to everyone else, it tends to be a group matter in practice anyway.
The actual running of the game and rules decisions again are technically the province of the DM. However, the fairness of a given rule decision or houserule is open to group consensus, and the feedback sessions we have at the end of every week's RP will sometimes cause a DM to change gears.
Of course, in the opposite direction, the players are willing to play along with the DM too, since the DM's taking the time to dream up the story. For instance, often when one of our DMs worries about motivation for the PCs in a campaign idea, the rest of us say, "Hey, you dream up the story you want; we'll cook up why our PCs would follow it."
As for paying attention to the plot, despite the fact that I don't DM - not because I don't want to or I'm bad at it, but because I'm horrible at thinking up plots for campaigns - I serve as the de facto group secretary, and there's been occasions where *I've* reminded the *DM* of stuff that's been going on in the game.
In short, I guess you could think of us as a round table board of directors... the CEO may technically get the final say, but only with a very large amount of feedback from everyone else. We're a group of friends as well as a group of RPers, so we're big on trying to make sure everyone's having as much fun as possible.
Peace & Luv, Liz