We stayed here at Casa di Adelina for five nights in May, 2011
I would recommmend Monticchiello as a base for that region, we did a lot of driving around and visited Montepulciano (twice) and Pienza and San Querico d'Orcia, and others. The driving was very easy and pleasant. As I recall the time from Monticchiello to either Pienza or Montepulciano was around 10-15 minutes.
About Monticchiello: a lovely, tiny old hill town; truly beautiful, but dead, dead, dead. There are a few attractive shops (maybe 3 or 4). There are three restaurants in town, among which "La Porta" has garnered some kind of a reputation.
We ate at La Porta four times, once for an afternoon snack when we first got there, and three times for dinner. I think the place is over-rated, good, but over-rated. See full review in restaurant section. We also ate one evening at Taverna di Moranda, which we enjoyed very much, although we were the only customers in the place that evening.
I also thought that Montalcino was not interesting nor attractive. Their wine is great, but the town was not worth much ( I may be wrong, based on one short visit).
All the other places we went were great, beautiful, fun, interesting.
About Casa di Adelina: first, hard to find in that tiny little town because all the street names were messed up on all the mapping services I looked at. The closest idea you can get is apparently on Google Maps, they show approximately where Casa di Adelina is. Use your cell phone.
The B&b is very nice with an excellent, light breakfast offered - too light for me. But to get in or out of the B&B you have to use about 50 steps - it is on the third floor of the building. The little house owned by the same family, Cocca, has door right at ground level in a tiny piazza close to the main entrance of the old walled town. Also, you must leave your car in a lot (free) about 100 yards down a hill from the main entrance, except when loading or unloading. The Casa di Adelina host is a very nice, smart, energetic young man who will do anything to make you comfortable.
On balance, we were very happy in le Cocca - it was just what we wanted, ground floor has bedroom, nice bathroom, well furnished kitchen and small living room. everything well furnished, bed was excellent, quiet as a tomb. Upper floor has bedroom and bath. We did not use the upper floor.