I wish someone would do the advanced Postgres version of the standard RDBMS "library" example as a book, going beyond just joins and simple window functions to arrays, json, notifications etc.
Greg Smith, the author is a former colleague and friend. His book on the performance side is definitely one of the better ones out there, but it's a few years old now and definitely more about tuning disks and storage more so than advanced usage. Sadly, I don't have a better one to recommend for the advanced user.
Can you tell him that I really enjoyed the book!
Definitely there's a market for postgresql books. Specifically, books with laddering type of learning experience (e.g.: beginner, intermediate, administration, developer, etc).