>In the projects page put up for Google's Summer of Code, there's an
>entry for filesystem ACLs based on the posix1e specification.

I don't know the answers to your questions, but back in 2001
(last time I recall ACLs being discussed), kre had an excellent
proposal for addressing associated data in general (ACLs would 
simply be one kind of associated data), I'd really like to see 
something like that implemented:

http://mail-index.netbsd.org/tech-kern/2001/03/09/0013.html

--sjg