The getAbstract book summary service has saved me a lot of reading time over the past couple of years (see my initial review here). They also offer audio summaries on a limited number of titles. I recently decided to download a few and test drive this content delivery option.
The audio summaries are delivered as unprotected MP3 files and I was quickly able to move them to an SD card for my no-frills player. Each summary is about 5 to 10 minutes long and read by a man and woman combo with pleasant voices. It's a great way to sit back, close your eyes and focus on what's being said.
The audio option isn't currently offered for the entire getAbstract library, unfortunately. It looks like they're in the process of creating new recordings though, which will help reinforce their position as the best book summary service available, at least IMHO.