This past fall semester most of my professors didn't require us to purchase textbooks, which was awesome! The flip-side of that awesomeness was that they posted everything we needed to read on the internet, which we then downloaded and printed out (if we wanted to). I prefer to print things out and take hard copies with me to class and highlight/write notes as I read. I am old school, I cannot retain information I read on the computer as readily as I can when it is in my hand.
As an experiment, I collected and kept everything from this semester, this includes mandatory readings, assignments and study materials. I am not certain how many trees had to die for my education, but it does beg the question if buying a book would have been better for the environment...?