The Zombie Stack Exchanges That Just Won't Die
What kind of questions are appropriate to ask for somebody who works at a book store?
Example subjects:
Ambo100
Libraries are not about books but about organized collections of documents. Book store questions may be on topic same as file management questions. For instance you could ask about how to manage your private collection of images. How about questions abnout Picasa, Flickr, Youtube etc.? These are all digital libraries as well. I am fine with book store questions but it's not the "book" which makes these questions on-topic, but the collection of books.
Book stores have a completely different motive than libraries and they exist in a seperate ecosystem too. There is some overlap but bookstores in general would probably be better served by going to a more general "retail store" type forum. Libraries have their own niche apart from book stores and thus I would say no such queries are not on topic.
I'd say yes, in fact, bookstore were some of the best "libraries" for some collections (for example, tech/computer books), but the fact is that they're rapidly going away, and likely will completely go away within the next 3-10 years.
All of the sample topics posed could equally come out of the public library setting: from the discussion of most user-friendly classification, to the perennial need for book/item displays. My library looks to bookstores for event & marketing ideas. As Jacob pointed out, both places are trying to organize and provide access to content. Aside from questions about how to liquidate 50 boxes of unsold holiday merchandise, I can't think of an inappropriate question. (Even then, I would say take it to your local library and they will use it in craft-time!)