Sounds cool. I would be interested in following this project. It's of particular interest for larger companies and there are vendors like chargeback.com (now part of sift) tackling this but I'm not sure there is a solution for the lower end of market. Source: over 2 years ago

Downpour.com allows people to download normal MP3s of purchases. They offer old-school CDs as well. So, no vendor lock-in there :). Source: 6 months ago

I agree about downpour.com - the vast majority (at least 99%) of the titles listed have no copy protection, so you don't have to worry about playing them only on a specific piece of equipment or specific software - any program and/or any device that will play MP3 or M4B files will work (plus you can play it online from their website). Source: 12 months ago

Downpour.com - multiple choices for downloads. Source: 12 months ago

Besides downpour.com, there is libro.fm which supports independent bookstores and has DRM free files you can download and use freely. Source: about 1 year ago

Incorrect, downpour.com will let you download MP3s of audiobooks that you buy. Source: about 1 year ago