We stayed in Berlin for a leisurely long weekend, and stayed at the Berlin Habitat because it was cheaper then hotel and close to the center, with an underground station within 3 min walk (it was winter, so every minute counts). Berlin is a lovely city that can be toured with public transport, so we did not rent a car at all, and only took one day tour to Potsdam.
The apartment was a 1 room with kitchen, and a bathroom. It was exactly what we needed. We met the owner, Stefan, at the next building where he lives, and he got us in. Since he had spent some time in the States, his English is flawless. He also was very informative about local issues. Place was clean and airy, with plenty of light.
As long as the price stays reasonable, (60-70 euro per night), It is a very good alternative to a local hotel. The supermarket is just 3-4 minutes' walk as well, and food there, including cooked, is relatively cheap.
ps - The apartment has free internet we mainly used for Skyping and search for Berlin restaurants using our laptop.