Where can I find resources to learn about the internals of Mac OS X?
Unless you've already found it, how about something like The Mac Hackers Handbook? It seems to have been published in 2009 and references Leopard in the description, so may also be a little out of date, but from the reviews seems to have a reasonable amount of information about security and OS X internals. May be a bit left field for what you want though...?

Or for something newer (due to be publishe June 2012) how about Mac OS X and iOS Internals?