I usually only have 1 for fun book at a time but might read other info books like learn how to garden or run better at the same time. Though the info books I don't read straight through like a fiction book. Usually just peck away at interesting bits as I need them.

I generally read too fast to really need more than 1 book at a time. Most books I finish in just a few hours and usually in one sitting. That and I am just too wrapped up in the book I'm in to want to even try reading something else.