Hello.
I am not sure if you are not mixing two kinds of memberships. First is Membership according to
http://devnet.kentico.com/docs/6_0/devguide/index.html?membership_management.htm, and second type is new E-commerce product type, Membership:
http://devnet.kentico.com/docs/ecommerceguide/product_type_membership.htmAs for how to filter product list for individual users or roles, you could use "Display to roles" property of the Product list web part, or use custom macro for setting "Visible" property.
Could you please consider all written above and provide some particular example of what you want to achieve? Thank you.
Best Regards,
Radek Macalik