I work with a blind guy who has shown me the merits of playing back at twice the normal speed (his screen reader is set phenominally fast and he listens to books not much slower... still much, much slower than I read, however). One joy for him is unprotected ebooks... text-to-speech on DRM'd books is generally impossible, although it is legal here for what little that is worth.
So now I'm starting to listen to books and using
www.foobar2000.org and the soundtouch plugin. It's also fun to vary pitch and speed independently

I'm finding that lifting the pitch a little helps, but doubling the speed makes the books much more ... um... listenable?