Login Suggestion for 5.0
On the showproduct page, rather than just blank the drop down for product options, or remove the user action links at the bottom of the page, why not add a link to Login in with a message, "Log in to access features of this site" or whatever phrase you want.
If the user is registered, it keeps them pointed in the right direction. If they are not, they'll at least know they need to register when they click the link and are taken throught the login/registration routine.
Just another thought.