In a j1.5 site I've published a userlist and set it viewable by registered users only.
I have a menu link to the list which is set to public.
When a guest clicks on the list the message "There are no published userlists" shows up. That terminology for this situation is incorrect. There ARE published userlists, just that you must be registered and logged in to view them.
The message should say something like "Please login/register to view userlist."