book_access_init()

I quickly read through the code in CVS. Looks good.

I don't think you need this function. It seems to be in place for anonymous users and cached pages, but enabling your module should clear the cache and rebuild the permissions to those nodes.

Not sure why this is in forum_access module. I don't use it for Domain Access, but I haven't done extensive testing of node access modules and cache.

og_init() doesn't do anything like this either, and it's the mother of all node access modules.