I printed out the first PDF I bought, which I can't remember the name of - it was the print version of Pools of Radiance (the computer game), but it had a different name, Ruins of something.
This was back when Wizards was selling them, and they gave me a coupon worth $4 off my next order. (Pdfs were $3.95 or so back then). So I got the biggest PDF available, which was the original Forgotten Realms setting.
I tried printing that out, but it ate up both inkjet cartridges about 1/3 of the way through (and I was using 'economy mode').
So, the upshot of it is, I stopped buying 2E pdfs, and the occasional d20 PDF I've bought, I just printed out the important bits, like character classes or tables.
I would print them out if I could afford it, but mostly I just read them on screen. (I don't like it, though, PDF format is not the best for on screen. Some enterprising company should try the Microsoft ebook format.)