1) After a successful registration, the "landing page" menu does not refresh to show member only menu items, so it is somewhat confusing to the newly registered user as it kind of seems like "nothing changed".
Once you go to a different page - the site home page for example, at that point the protected menu items then appear.
2) It seems like it would be better to have the user complete payment first THEN create a username and profile.
3) During the user name/profile creation, if a user attempts to use a name that is already in the system or an email, it gives no indication as to what is going on - it appears that the site is "broken" because all that happens is the screen refreshes and drops you right back in the same place, less your passwords...
Keep up the good work