Agreed. I only recently started listening to audiobooks--I download them for free from the public library and put them on my MP3 player. They're great for dog walks and other exercise occasions. Lately, I've been working my way through a very nice production of Dune.
A little off topic, I guess. But yes, audiobooks on an MP3 player would be my choice for the treadmill over TTS ebooks on a Kindle.
On the other hand, for my last birthday, I asked for a portable DVD player. I have it hanging in front of the seat on my exercise bike.