My good mate Reino pointed me to a great little GUI ACL editor for Mac OS X. More useful on non Server versions of OS X that lack any meaningful way to edit ACLs other than via the command line, it could potentially also be useful on OS X Server if you’ve got some weird ACL issues happening and need to see a bit more about what’s going on.
Check out Sandbox:
The documentation says it’s been updated for Leopard, the download looks like it was last updated around a year ago, but it seems to work perfectly on 10.6 as well.