I flew from Chicago to Munich on United, leaving on 28 November and was supposed to fly on to Berlin on the morning of the 29th on Lufthansa. When I arrived in Munich, my flight had been cancelled and the airport was chaos because of snow (perhaps 1000 people in line to change reservations).
My luggage has now been missing for almost a week, and I can get no info from either the Lufthansa or the United phone lines or website. They have been profoundly unhelpful, and keep telling me to phone back. I have now sent the tracing form. We will see what happens.