My biggest peeve is that I cannot simply look for a book across the different libraries I have access to. I have to select each one individually and repeat the search several times to find out that the book I am looking for is not available.
Finally, I wish there was a simple list where I can store books I am interested in without committing to it. The tag system can be used that way but is unpleasantly wonky. Why not make that a menu button rather than the 'timeline', which gives me an overview of the books I signed up for, loaned, and return dates for, I assume, the past 100 years. Why would I need that information as a top level button?