I wanted to strongly suggest a resource that turned out to be invaluable for us. We stumbled upon Origins Ethiopia Tours & Travel (originsethiopiatours.com) by accident, and were surprised (especially after the fact!) that it was not included in either your book, or the Lonely Planet series. Since my wife and I were meeting friends in Addis, we had not made plans to travel internally. At very short notice, Origins Ethiopia set us up with an extremely efficient itinerary along the historical circuit in the north, which went incredibly smoothly. Our drivers and guides were always early, friendly, extremely well-informed, and never overbearing. They each gave us the equivalent of a college-level lecture at each place we visited; they made sure that we had excellent places to eat (all of which were mentioned positively in the Bradt guide), as well as making sure that we always had interesting evening plans (at a nearby tej bet or azmari bet) before letting us go at the end of the day. Samson (who organized our tour) helped us avoid all sorts of touristic hassles: he was very clear about what time to arrive at the airports, about confirming flights, etc., and he twice picked up the phone to talk to us personally, when we had a mid-trip query.
Jonathan T. King