My partner and I stayed at One Washington Circle for five nights in January and would recommend the hotel to anyone who wants to be central for just about everything that Washington DC has to offer.
We (or rather my travel expert better half) booked the hotel online and got a great rate for Washington DC; something around $90 a night excluding a small amount of tax. For this sort of money we were prepared to compromise a little on the quality of the accommodation as the hotel is so well sited for everything we wanted to see. Well, we were very happy with what the hotel had to offer; the reception staff were very friendly and helpful, as was the doorman. The rooms, or I should say apartments as I have read that this place was once an apartment block, are very well equipped - we had a separate bathroom with every extra you could want in terms of toiletries, hairdryer etc. A large bedroom/lounge with two double beds, television, safe (which for a pleasant change from Europe wasn't charged for), telephone, free internet access via ethernet cable, and finally a large balcony. We also had a great kitchen which had a cooker, microwave, fridge/freezer, and all the cooking implements you could use including most amazingly a coffee grinder, coffee machine and free coffee beans and condiments! I made fresh coffee every morning which was really lovely and nice to drink whilst looking over the free Washington Post which is also left outside the room every morning.
The room is cleaned very well every day and everything used is replaced or cleaned; the coffee machine I mentioned was completely dismantled and washed every day and the cleaner even left more of the sugar etc that I was getting through a lot of - very thoughtful. As was the mints they left at night - although they forgot us on a couple of occasions. One other small point; they leave you a dressing gown/bathrobe, but only one which doesn't make much sense in a room with two double beds.
I ought to mention noise here; some reports talk about noise from the hospital located on the opposite side of the roundabout which is outside the front of the hotel (and located next to the Foggy Bottom metro station). Our room was down a side street and a few feet from the hotel front, and we didn't notice any noise at all really. We have stayed in many hotels in European cities where the noise is pretty bad nearly all night long - not here though, and the ear plugs that I'd packed as a precaution stayed in my bag.
One small point; we didn't try the restaurant or bar but apparently they are good - certainly the chef has a good CV if you look at their website..
As for the position of the hotel - it is pretty much perfect for all of Washington DC. Basically you are at the upper NW end of Pennsylvania Avenue and about three quarters of a mile from the Whitehouse and most of the middle of Washington. If you don't want to walk (and we did quite happily a couple of nights), then you can stroll across the roundabout at the front of the hotel and get the tube (Foggy Bottom metro station). This station has access to lines that will take you into most of the downtown stops which is good for shops/museums etc including the famous Mall where you can see the Washington monument, the Lincoln memorial, Capitol hill, and all of the big museums. These are all a few minutes away on the metro.
The metro network also takes you further afield, and with a metro train and bus we went to the Potomac Mills shopping mall; this is really huge and great for bargains.
If you walk out of the hotel and head the other way up Pennsylvania ave (in a roughly NW direction) then you end up in Georgetown within a few minutes - you really do have to walk this as there is no metro station there. We didn't know much about Georgetown before we visited Washington, but it turned into one of our favourite places for shopping and food - it has some lovely old buildings and really good restaurants (including a great pizza place). There is a small but really lovely shopping centre on the south side of the main street that we didn't notice until the last day.
To conclude then; One Washington Circle has very good rooms and service, and is a great location for all that Washington DC has to offer.