Over at "Read, Write, Now", Peter Kerry Powers comments on whether or not listening to audiobooks is reading. Read his posts here, here and here. In the comments section, Hugh McGuire, the founder of Librivox, takes up a defense of Librivox and audiobooks in general. It's a superb debate, the quality of which you rarely see on the internet, with good points made by intelligent, informed people on both sides.
My own view is that sitting down in your comfy chair and cracking open a new hardback is not the same experience as listening to the same work of literature in an audiobook format. But neither is reading the same book as an ebook on a PDA in ten-minute intervals on the subway. Or skimming a highlighted, underlined, and annotated used paperback while preparing for a college class discussion. Or being ushered into a library's rare books room, being issued white gloves and studying the original manuscript.
We read in many different ways for many different purposes. I'm not sure when exactly the distractions outside the text stop the experience from being reading and when it starts being merely receiving a collection of words. I think that the answer is in the mind of the reader rather than in the medium. I read paper-and-print books at home, but I also listen to audiobooks on the train during my commute to work. If instead I were listening to books in the background while doing something that required a larger portion of my concentration, I wouldn't consider that reading. When the words on the paper or the reader's voice disappears, and I'm completely taken away from where I am, that's what I consider to be reading and that doesn't depend on the medium.