I've often wondered why so many libraries tend to have odd/obscure works by famous authors, but not the books that they're actually famous for. (Clarification: I mean the famous books aren't even in the collection, not that they're merely checked out by someone else.)

Also, this is a not a comment on the NYPL, which I've been to only a handful of times a long time ago, but I've been really disappointed by too many books in too many libraries being really trashy and in poor taste. I'm not sure if it's a matter of the library just catering to the lowest common denominator, the book collection reflecting the community's donations, or of the book selectors themselves being poorly educated and having trashy tastes, but it really makes me scratch my head sometimes.

University libraries and private libraries tend to be much better in this regard, with public libraries being typically way worse.