Ever since I first started using bookish sites like these to over-organize and sort my books, I've always thought it'd be nice to have the option to give your shelves a description. Especially nice for shelves with cryptic, witty, or otherwise non-direct names.
For example, I've got a shelf called "I Might Be British" that I use for my books about British culture and other quirky British history topics. I know exactly what it means, but someone else might be clueless as to what exactly it would contain... British Literature? Books by British authors? Books that I would only read if I were, in fact, British?
Not only would it be nice for other people to see what your cryptic shelf contains, but also for inputting criteria that you have for that shelf... if anyone's like me, I always find myself fudging the meaning of a shelf simply so I don't have to put a book in my "Everything Else" shelf. If I had a place to input specific criteria, I'd probably end up with more accurate shelving for some things.
Maybe this could be an optional option that would show up if you hover over the shelf name? Or just something that shows up when you click to that shelf? A privacy option would be nice as well, so you can hide criteria, or (although this defeats the purpose) explanations.
I know I don't have my shelf accessible from my blog, which is how I like it, but I do love to over-qualify things, whether it be for myself or for others (as I'm doing right now), and I think that having a shelf description box would be a very useable option for everyone.