Just back from a trip to Ethiopia which included three nights in Lalibela. We stayed in the Jersualem Guest House and loved it. Big rooms with a lovely balcony. It was clean and the restaurant had the best salads we came across - lentil salad or mixed salad can be personally recommended...
We had a great guide - Fikru Giorgis - atofikru@yahoo.com if you need an english speaking guide he comes highly recommended. The Bradt Guide people use him when they come to visit.
Churches are incredible - still trying to get my head wrapped round how they built them.
Three days should be loads and even gives you a chance to head out of town to some other great sites in a half day trip.

