There's a similar thread at CPAN shared by multiple users. It's a decent start, but there is a problem if you want shared groups, and group ownership propagation on directories is based on the set-groupid bit in the parent directory (rather than on a file-system-wide mount option). The set-groupid-bit gets cleared by CPAN installs, so group ownership of sub-directories can disappear. I filed a bug report, but haven't heard anything. I also wrote some scripts to coerce the ownership and permissions back into something more reasonable. I could post them, if there's interest.