My wife and I stayed at the Soho Hotel about a year ago and loved it. Gorgeous, charming room, great service (for London), and we loved the location as we spent a lot of time walking around the neighborhood and beyond. The concierge was also very good with our requests such as arranging our transportation to the Fat Duck, etc. It's not a large hotel, and we enjoyed the coziness of it. The library is small, but comfortable, and the drawing room is great for tea and reading the paper before you head out, or a drink at the end of the day.
Do note that occasionally there will be paparazzi posted at the entrance as that happened once during our stay. Apparently the cast of "The Imaginarium of Doctor Parnassus" was staying there for the premiere, and one afternoon an event promoting the film was held in the library, which posed a minor inconvenience. Seeing "Mini-Me" roaming around, however, perhaps made it worthwhile.
One perk we enjoyed was on more than one occasion we stumbled across another Firmdale hotel during our walks, and as a guest of the Soho, the other hotels gave us guest privileges there as well, and we were also able to charge our drinks or services back to our account at the Soho, which we thought was a nice gesture.
Overall, I highly recommend the Soho.