When I'm a player, I'm in the minority. You could give me a 50 page document about your world and I'd read it, print it out and bring it with me to the game. I'd rather be immersed in the setting but as others have said most players aren't.
I think keeping it to a paragraph or two isn't enough though, depending on the setting. That might work for something reasonably generic like FR or GH, but if you were running post War of Souls Dragonlance or even something different like Eberron, I think players need to know a little more than that to understand the setting they are getting into.
The setting is as much of the game as the mechanics, so I'd expect players to take/want to take some interest in the setting they are playing.