Mixed Review
My husband and I used Starwood award points to book a stay at the W Hotel for a weekend we were visiting DC for a friend's wedding. We are in DC frequently and typically stay at the Fairfax Embassy Row at 24th and Massachusetts. I wish we had done so this time instead of wasting 60,000 award points on a sub-par experience. 
I will say that the hotel is beautiful - they did a great job with the renovation from the old Hotel Washington - and it is in a very central location if you are in town to sightsee. However, I think we got the crappiest room in the entire hotel (room 931). Our only source of natural light was a frosted window that looked into an air shaft, which was very frustrating given the amount of award points we were spending and that we are Starwood Gold. 
Generally the staff was very friendly and accommodating, with one huge exception. After getting back to our room late on Saturday night, we were famished and wanted to order room service. We could not get anyone to answer our calls - not the front desk, not Whatever Whenever - no one! We finally had to call the Starwood Gold line to get their assistance in getting someone on the phone who could take our room service order.
Finally, be aware that the valet rate here is $50/night. Yes, the hotel is located right by the White House so it is not going to be cheap. But you can find a much more reasonable overnight rate at one of the many nearby parking garages.