It's only the main quest. I am not being flippant, it's just I assume the guild/faction quests will be more interesting, and would prefer your actions in these to alter the nature of the guilds, whereas the main quest is usually save the world, or die trying.
I don't know what to think about the main quest to be honest,as regards mulitple endings. I'd probably say no to mulitple endings,but i'm not fully closed to the idea.
I agree with zen though,the faction quests do hold alot of interest.I can't wait to see what they are doing regarding this in skyrim. And who knows,maybe one of/or more of the factions could play a part in the main quest.