I ran my first campaign in....lessee, 2000 I think, using my Azeria homebrew. I didn't want to deal with stupid people who knew more (or presumed so) about Greyhawk or Forgotten Realms and then presumed to tell me I was running things wrong, ruining this or that, completely misportrating such-and-such, or otherwise messing up their favorite campaign setting. I really hate people like that, so closed-minded, without any ability to just enjoy the game and go with the flow; not like I was going to be an RBDM or something, but the only way to avoid people ranting/whining like the above was to run homebrew. Avoided the problems of player knowledge exceeding DM knowledge, lack of mystery or whatnot, and conflicting ideas about what the setting was about. I'll run a published setting (well, besides T13K, which I already run games for, as it's fairly small and thus not a problem) when I'm confident enough in my familiarity with it to not botch it up in front of more experienced players.