BONUS ROUND: Our department is considering implementing some level of custom classification to our specialized collection focused on local history. Here are some examples I have found of libraries doing just that (or having done that in the past. Please share your experiences if you know of more or especially systems for a particular topic (like history and genealogy).
Hack Library School interviews two librarians regarding cataloging and metadata. Most important point is that knowing where and how to find the information (like RDA toolkit and other resources) is more important than knowing it all right out of the gate.