My girlfriend and I went on a very short trip to Berlin, and David and Nicki were very helpful and gave us some great tips for what we could do and see during our stay. They also suggested and helped us find a bike rental place, which ended up being a huge benefit to our getting around the city instead of using public transportation.
The communication between us was great and they were flexible with our check-in and departure times. They are wonderful hosts and great to talk to, and they even offered for us to join them out with their friends. If we had had more time in Berlin we definitely would have joined them - we would certainly stay with them again the next time we visit the city!