There is an interesting article on w3.org about names and websites assumptions: http://www.w3.org/International/questions/qa-personal-names
* What is your full name, including title? (e.g. Mr John Jules Smith, Señor José Hernández Fernádéz, Kim Ban-Moon)
* How do you wish to be referred to? (e.g. Mr Smith, John, Sñr Hernández, Mr Kim)
* How should we address you? (e.g. Mr Smith or John)
Which covers the Icelandic given-name first scenario, as well as the matronymic vs patronymic issue. This puts the person in control of what to sort on, while how to sort it would be controlled by the active user's culture settings.