I voted 4-5, but I probably should have voted more now that I think about it. I am always in the middle of 2-3 fiction books, at least 1 technical/trade book, and a philosophy book or two. Then there's the audiobook collection, which I might be working through an additional 2-3 books of assorted category and character. I also like to sample a chapter or two of many books as I go, to see if I will want to read them later.
I am also very fickle though, and will sometimes walk away from a book for months before picking it up again and finishing it later in an all night reading binge.