AFAIK, everyone that interviewed during my week Dec 5-9, had to wait at least 10 days to hear back. Being that you interviewed then and you dont think there were any problems with the interview itself, you probably got lost somewhere (not you, your paperwork). Might be too late as I know they are interviewing for the Feb class this week. Only thing I could think of is you were at the bottom of the stack (only because you were the last to interview) and probably filled all Jan slots by the time they got to your name. Just my guess. Keep trying.