Hmm, have to think. Started to go into "features I'd want in an ebook store," but that's not the same as questions.
Problems: Geo restrictions, DRM: these need to be *clearly marked* and *explained*.
Software & hardware compatibility needs to be clear, too.
Customer service/tech support need to understand how ebooks work; need to be *quickly* responsive to issues like "right title; wrong contents in book."
How will your store deal with a constantly-growing number of types of ebook readers, whose owners may not understand filetypes and only want to know "can I read this book on my device?"
Refund policy--do you have one? How does it work?
Do you have a way of contacting publishers to get them to fix badly-formatted or wrong-content ebooks?
(If they're dealing with the new agency model): How will your store stay competitive, if you can't offer lower prices for many books?
How do you deal with international customers? Do you have a way to hide content that a particular customer can't buy, and if not, is it at least clearly marked?
How effective is your search engine? Your browsing ability?
What features make your store better for its customers than the other ebook stores?