With the release of 2.1 the menu structure change so that admin level users got a User menu and subscriber level users go a Profile menu.
If you use add_submenu_page and specify hooking into users.php this works and is only visible to admins.
If you change this to hooking in to profile.php the menu is visible to subscribers under Profile AND admins under Users.
I don't think it should be visible to admins as profile is not a main menu for admins so how can you specify a submenu?
This issue is affecting my plugin quite drastically as I dynamically link to this page from within the content of the blog. It's impossible to specify the link if it's moving!