Firsthand I vote for the formal "Sie" (as well as avoiding directly addressing the user where possible). We will have a lot of non-students using this system in Heidelberg (professors, staff, administration, etc.) and I think that would prevent problems. I would like to hear what others think about this. I would also be interested to know what MS (and other translated) Software uses (I am in Texas at the moment and do not have access to a German MS software to check).