I stayed at the Ankober for two nights in October 2012, after opting out of our tour operator's choice (the Taitu, which I absolutely do not recommend).
It's a small place, about 10-15 rooms, which makes for a personal atmosphere. No problems with cleanliness of the rooms or the public areas, and the shower was a miracle for a guest house or even a hotel in Ethiopia - hot water and very high pressure. Marvellous!
There is no bar or restaurant, but as the Ankober is in the Piazza this is no problem at all. Noise is no issue as the guest house is situated down a quieter street, away from the noisiest bars and clubs.
I take one star away because the morning taxi did not arrive as booked to take me to the airport, but otherwise - highly recommended.