SVN::Notify is a wonderful post-commit hook, and we use it for all of our subversion repositories. One of the awkward things about it in our environment, though, is that the "--from" and "--to" arguments have to be maintained. This means that we effectively have a duplicated list of authorized users, as we also use an AuthZ-style file.
I've written a little script that helps with this, by automatically creating the --from and --to args based parsing the AuthZ file. This seems to work well... Give it a try if you like!
http://www.borlik.net/blog/archives/000182.html