[kbs666]

I love physical books but
[Scotty voice]me back cannot take the strain[/Scotty voice]
So I buy PDF's and load them on to a flash drive and then load that on whichever device I take gaming or access the PDF's on my desktop when I GM.

Note I don't run adventures from PDF or from printed sources. I write my own, always have and doubt anything is going to change in the future. I buy books for rules material and the like. The exception are a few classic pieces like TSR's Against the Giants/Descent into the Depths and Paizo's Rise of the Runelord's which every good GM should probably own and run at least once just to see what the true masters of the craft have done before them.