Books on Tape

Is anyone here an adherent? I've never used them because I fear losing something, but I've found that my desire to consume information isn't matching up well with the actual time I have available. My question is simple--how much, if anything, do you actually lose by listening to the book instead of reading it? Does it affect how your process information?

I gotta say, it might be cool to have Grant's memoirs on the Ipod while I'm knocking out my miles. I listened to David Blight's lectures while gaming or doing the dishes, and it was awesome. Any thoughts?