@Carpetsmoker
There is no such thing as Handbook for Solaris or OpenSolaris, but there are a lot of docs/books on
docs.sun.com, for example their book about Administration with Virtualization has 540+ pages and 42 chapters, and thats only about virtualziation.
I think that we just need to get used to other model of documentation then handbook:
http://docs.sun.com/app/docs/coll/47.23
Linux kernel does not have documentation at all and you have to check options.c for details.