There are four guilds. There's a thieves' guild quest that can get you in trouble for stealing from some loon in a tower, and I believe there's a dark brotherhood quest that may get you in trouble, too. It's been a long time since it happened, but it sucked. That's why this time, I'm finishing off the other guild quests first, though this last thieves' guild quest looks like it's a whopper; may save that 'till I have more magic.