If by reading it is meant "reading for pleasure" than I usually read just one or two books at a time. But otherwise, I've lost count how many books I am reading! There may be some I read because they are connected with my current research or project, some I started to read because I got interested in some subject, then some I started to read because I found out I needed more background to understand that subject etc.
E-reading certainly made things worse for me. With paper books there was at least some limit to the number of books I could have open on my desk at any given time. Ebooks don't have that limit!