This is not exactly a hostel. It is more like a cheap hotel or a dormitory for students. So the common area really doesn´t work like a hostel. But it is a nice place though. My room was pretty clean (despite the fact I killed a small cockroach in my room that flew through the window). Breakfast is good. Location next to the Glaciere metro station was very handy. Free wireless only available in the reception area. Wireless in the room is paid.
The hostel is located in Knightsbridge, which is quiet and nice neighborhood. The nearest underground station is about 10-15 minutes walking (Gloucester Road), but from there you have easy access to all tourist places of London. My room was very clean and bed was comfortable. Breakfast is average/good. The only bad thing was wireless reception. It was failing intermittently and signal strength on my room (2nd floor) was not great.
Cocomama is really a nice hostel. It is located about 25 minutes walking from the Red Light District, which for me was a plus since I didn´t wanted to stay near the crowded area. Everything was pretty clean and staff was helpful. I only missed breakfast (for the price of the stay, breakfast could be offered)