We stayed at Fonte Bertusi for 3 nights in October, 2012. We chose Fonte Bertusi because of its close proximity to Pienza (a favourite Tuscan towns) -- we wanted to be able to enjoy our dinners without the annoyance of a long drive in the dark afterwards. We stayed in the La Mandorlo apartment and were very impressed. The apartment was huge and was probably the most private of all of the available options. It was the perfect place to relax and recharge. I highly recommend and hope to return some day!
Many other reviewers have commented about the wonderful art in and around Fonte Bertusi. I should mention (not as a criticism, simply as something to be aware of) that the apartment we stayed in contained some pieces that travellers with children might not be entirely comfortable with.