I was at the Minerva for three nights in June 2012 -- and I'll start with the positives. The location was very convenient, and my window overlooking the Piazza Santa Maria Novella was lovely, as was the Piazza itself -- and of course the church, which was magnificent. We were there during the feast of Corpus Domini, and being able to listen to the midnight service over the loudspeakers into the public square was really special. Proximity to the train station was another plus. The rooftop bar and swimming pool were very nice -- it was too cool for the pool when I was there, but I enjoyed the panoramic view of the city all the same.
However, the hotel itself left a lot to be desired in terms of comfort. The beds -- yikes. They were simultaneously hard and astonishingly lumpy. The lumps in the mattress were visible even through the comforter -- I mean, they were BIG. The hotel can be confusing to get around, with some corridors and elevators not heading to where you might think, and the staff is not particularly helpful.
The food at the hotel restaurant was very tasty, but the head waiter did not endear himself to me when he was rude to an elderly gentleman in our party who did not clearly understand the Italian menu and asked for clarification about an item. The wait staff at breakfast was also less than pleasant, which was something I didn't encounter anywhere else during my stay in Italy.
I'd love to return to Florence -- but if I do go back, I'll be staying elsewhere.