This has finally annoyed me enough to add my comment to the thread:
Please, PLEASE let me set a 'preferred file type' to my account so I can set it to epub. Not only is it annoying to have to manually set it every single time I check out a book, I also grumble at the 'free advertising for Amazon Kindle' button. Why are my tax/annual fee dollars supporting vendor lock-in?
(and I second pretty much everyone else's feature requests if the folks from Overdrive are still lurking.)