I have three or four books going at a time, so I'd have to say multiple. Read one for a few days, trade off to another and then go back to the first book or so on. Currently have A Dance With Dragons, Ender's Game (second time now), and Confessor (Terry Goodkind) going on.
How do you keep up with them all? Better question. Are you enjoying them all equally? For me a book is like stepping into another dimension. I am the characters. I feel like jumping from story to story would lessen that emersion. That's just me though. I wish I could read like that.
Yeah I enjoy them all equally. I never do this with a book if it's my first time reading it though. Yeah I look at it like all the books I own are in their own contained universe, and moving from say ADWD to Ender's Game is like going from... Our dark ages to our future... Make sense? Sounds crazy to type it for all to see like this though.
That's a great way to think about it. Where have I heard that before? Some show or film where they wandered in and out of classic books?