For me a PC copy is awsome for referance and for copying certain sections I may want to bring to the table, but absolutely atrocious for reading. Especially the adventures. They require way to much flipping around to make a pc version truely helpful for the adventure in its entirety. Plus, I simply prefer a magazine copy to read.
With a paper copy I'm not tied to the basement, where my pc is, for an hour while I read the things. I can sit in my backyard in the sun and read while I watch my son play. That is useful product to me as a consumer. The PDF is simply a handy extra.
My pathfinder subscription comes with a free copy of the pdf of all the paper magazines I receive. I have access to them sooner that the paper version and so far I've used the PDF's once, and that was in game so I could extract some images of notes the PC's were to find.
I'm on the fence with the 4th edition, some things I like, others not so much. A paper copy of dungeon and dragon for me to read and help me to kindle that into some "Oh I've GOT to run THAT!" moments would probably get me off the fence and get me running some 4e, and buying more products. But pdf's of a magazine aren't a product I'm interested in, and won't purhcase. (Which is not to say I won't purchase gaming related pdf's. I have and have enjoyed them for the short rules additions they were.) So, I continue to look over the 4e rule books and continue to sit on the fence.
-Ashrum