We stayed at Karsten's place for three nights. Everything was perfect - he even offered to meet us at the airport.
His place is spotlessly clean and has everything you need for a visit to Berlin. It is very close to public transport, there are great cafes, bars and shops nearby and you can walk to the city centre if you want.
The main bedroom and lounge room is huge, with the biggest bed we've ever slept in and a lovely sofa. The large windows made it nice and bright, and the shutters and curtains made it cosy at night. The kitchen has everything you need including kettle, cafetiere and toaster. The bathroom is lovely too and Karsten provided toiletries and other nice touches.
Next time we are in Berlin hopefully we can stay at Karsten's place.