Despite the fact that it technically wasn't supposed to be released until today, Nordic Games quietly released Spellbound's Arcania: Gothic 4 - Fall of Setarrif expansion pack on GamersGate, Steam, and likely other digital retailers sometime yesterday. Both the aforementioned sites are selling the add-on for about $15, though Steam also offers a Gold compilation with the original game for $30 and has included Fall of Setarrif in their Gothic Complete Pack for $50.
If anyone gives this a whirl, please drop by our comments and let us know how it is.