I find that it works well when I use the LONG sitename URL https://sites.google.com/a/webarts.ca/bzsupreme
But NOT when using my custom domain DNS redirected name http://bzsupreme.webarts.ca
A few hours and hair pulling looking at all the sharing settings.
It already has a bug registered for this - http://code.google.com/p/google-apps-script-issues/issues/detail?id=546It
over a year ago.
Come on Google fix this.
For now my DNS zone provider zoneedit.com has a "Web Forward" feature that redirects the URL for me. Its a workaround.