Anonymous users are nothing to worry about - we even like to refer to them as Guests!
iPhone apps have a clause that means that a user must be able to skip registration before choosing to sign up with their email address. Some users will sign up anyway without skipping, but others may choose to have a browse first.
An anonymous user (or guest) has a limited experience compared to registered members, and if they try to do certain actions such as commenting or posting themselves, they are pushed back and prompted to register.
Most anonymous browsers will convert into registered users once they see your amazing content anyway!