In the Set Reserved Names section, add 'User' and 'Superuser' as default values. I have a person who once used Superuser and then added red squares in his title verb. People thought he was an admin. Rather cheeky of him. :D
In the Registration Settings, option 'Method of registration employed for new members' has a default of 'Immediate Registration'. Seems to me the default should be 'Email Activation'.
Actually I always wondered a bit why the default is "immediate", when this is (or should be) kind of unusual.