Same here. There are University discussions that I've downloaded that are four to five hours long and they've been re-listened to 10 or 12 times. I have my MP3 loaded with seminars and sermons rather than music.
Some people would feel bad for me. I love listening to people expound their ideas on the fly, whether I agree with them or not, at the very least I can look for the philosophical underpinnings of what they're trying to sell.
Anyway, that was way off topic.
I do pretty much the same when it comes to mp3's Adam. I have lectures on video that I have to watch as well, but the mp3 audio can be listened to most anywhere, while you're doing most anything. I'm a voracious reader and have a plethora of text via hard bound books, e-books, and even pdf files for study.
Videos are ok, but they consume a lot of time (especially if I have to download them ).