Morgan Stanley asked 700 tablet users about tablet use and their printing habits. As it turns out, 46 percent of those surveyed said that they printed less while 13 percent indicating that they printed 16 percent less after owning a tablet. I assume the options of "printing somewhat more" and "printing significantly more" were available for the survey responders.
It can also be pointed out that printing/writing paper demand in the U.S. has dropped 9 percent since the iPad was first released in April 2010. Overall, paper demand is down a total of 24 percent since it reached a peak in 2006.