We stayed at the Park Lane Hotel, a Starwood Resort (SPG Category 7!) We used 160,000 Starwood points for a junior suite for 9 nights. During those 9 nights, the 5th night was free. At that time, this junior suite conservatively cost about $350 per night. We saved about $2800!
The suite was huge!!!! I mean huge!!!, the biggest room we ever stayed in anywhere. The hotel and rooms were a little dated (or maybe that is how it is in London), but the hotel was 2 blocks from the subway and a 5 minute walk from Buckingham Palace. We were in London, we barely spent any time in the room anyway. Just to sleep!!!!
Note, that originally when I went to book this hotel on points, this junior suite did not come up on the SPG website. I actually called and got a live person who booked this suite for us. If you are not happy with what you see on the website, call. It can make a difference in what you can get.