We stayed here overnight after arriving from the UK, as we didn't want to pick the hire car up until the morning, and it suited our needs perfectly.
The free shuttle bus from the terminal runs every 10-15 minutes and it is only a short journey to the hotel. The hotel is large with nearly 400 rooms, it seems bigger because it is only 3 storeys high, so covers a lot of area.
We got a nice corner room on the third floor - very well appointed and very clean. It was quite a trek to the concierge lounge, but once there the lounge was very nice - it served a nice pasta meal in the evening and a very nice breakfast in the morning.
We got a good nights sleep in the great Marriott bed, and weren't bothered by aircraft noise at all.
If I have any niggles, they are that the indoor pool was COLD! and that there isn't much else around the hotel - the latter is completely unsurprising, given its proximity to the airport. I understand that they do offer a comp shuttle to nearby shopping facilities, but we were only the the one night, so didn't take them up on it.

Anticipating a winter storm that would ground us and cancel our flight, my wife and I stayed at the Dulles Marriott for two nights in December, 09. We were both pleasantly surprised and pleased by the experience.

We selected the Marriott because we knew that the hotel was basically on the property of Dulles Airport. The hotel itself was not inspiring. It is a late 1950s/60s modern building. It is very large and is built around a courtyard. Indeed, when she first saw the Hotel, my wife thought I was crazy to want to camp out there during a snow storm to await the airport reopening.

However, on seeing our room, we both were quite pleased. Clearly, the rooms and the bathrooms have been updated sometime in the last few years. They were clean, well appointed and comfortable. The bed was very comfortable.

In addition, we ordered room service which was good (though nothing special) as well as having two meals in the hotel restaurant. The hotel was packed because of the storm and our meals were under “snow” conditions so the menu was limited, but they were both good. It was great to hangout in the bar with stranded travelers from around the world.

We used the gym facilities which were good.

If I’ve one complaint, it was that they didn’t have WiFi in our room and we had to go to the bar to get free WiFi for our computer.

On the other hand, the staff was great. Many of the staff members we dealt with were doing double and triple shifts because they couldn’t get home and their replacements couldn’t get into work. However, everyone was pleasant, courteous and helpful. There was a nice air of camaraderie.

We took advantage of the stay and park to leave our car at the hotel for the duration of our trip. The vans to the terminal ran constantly even during the storm. Parking was good and our car was easy to get to (and had thawed-out by the time we got back). In addition, the cost was better than the cost of round-trip cab fare into D.C.

In the end, we had a little mini-vacation at the hotel waiting for the storm to blow through. We were happy that we went to this Marriott.

We got the park and fly package the night before we left on a overseas trip. About $130 included Saturday night and parking for almost three weeks. When we returned we used Marriott points since the cheapest rate they had during the week was $240. The van to and from Dulles was prompt and the driver helpful. Everything at the hotel was, well, vintage Marriott: Comfortable clean room, cheerful helpful staff, no hassles and no surprises.