How many factions can I concurrently join in Reckoning?

How many of the major factions can I join in Kingdoms of Amalur: Reckoning? Does joining one of the major factions preclude me from joining another one in particular?

According to this interview on RPGamer.com, you can do all the faction quests in a single playthrough:

The player can make a lot of choices about the main character's story, but how much can we affect the world around us?

There aren't a lot of destructive branching paths in the story that lock the player onto a certain path or close off things in the game. Rolston used to think that forcing characters to make these kinds of choices was innovative game design, but he now sees them as too limiting. There are lots of choices in the game, but the consequences of the choices won't lock the player out of content. Players will be able to complete all the faction questlines in a single playthrough of the game if they so choose.

This speaks to the game's replayability as well. The game was designed in such a way that the player can replay it if they desire, but can also experience all the game's content with a single character. The ability to respecialize at will even allows players to experiment with the different Destinies and combat abilities on a single character.