I have really enjoyed the increased access to ebooks and audio books Overdrive has provided. My local library offers a good selection, and the ability to use the Overdrive app, Kindle, the web, etc., to access my content has been pretty great.
I have had problems with the UI - I hate how non-obvious it is to return a book once youre done with it (I think fixing this would make books available much more quickly...) but overall, its been a great app. Bugs have been fixed in recent releases, and it seems to be getting better.
FloridaSaint about OverDrive: eBooks & audiobooks