Very Average Hilton
My wife and I stayed at the Capital Hilton for the weekend because we were in town visiting my brother and were looking for a nicer brand hotel to enjoy a relaxing weekend. I'd like to caveat this introduction by saying that we used Hilton HHonors points for this stay.
The hotel itself is conveniently located on 16th at the Corner of K street. when we arrived at the hotel around 300pm on Friday, we were disconcerted by the fact that a sign was being displayed advertising that the hotel parking garage was full. My wife and I drove around for abut 15 minutes since we couldn't find a parking garage in DC that allows you to leave your car in it over night. (There IS one on 17th Street at K Ave that charges 25.00/night for all those of you who don't want to be gouged for the $42.00/night being charged by Hilton). We called the hotel that said they had a map of the garages in the area where we could park our car since their lot was full. Upon returning to the hotel I managed to convince the bell hop to let us leave our car up front and he'd park it when a spot opened. 
Check in was smooth and the gentlemen who checked us in was extremely welcoming. One thing I will give to the staff is that the majority of them were very up beat and polite. We were upgraded to a room on the 10th floor because we're HHonors Diamond members. This entitled my wife and I to free breakfast in the morning in the "executive lounge" which left much to be desired. The breakfast is a basic continental with some mini bagels, fruit (if there's any left), pastries, and cereal. The coffee was empty both days we went and we didn't bother waiting for it to be filled; we just grabbed Starbucks.
The room was nice and bigger than we expected for a hotel in the heart of DC. We were in a room right next to the executive lounge though and the traffic from people coming in and out throughout the course of the day and at night hoping that it was still open was pretty rough. The lounge opens at 630am, so we heard every person who walked by and didn't think to be considerate enough to observe the hotel's quiet hours. As other reviewers have noted, our housekeeping experience was limited. It looked like they made the bed and replaced the towels and left. Our dirty glasses were left and the melted ice from the ice bucket wasn't discarded of; to include making the room smell fresh. 
Overall, the hotel left a really average feeling. Not great, not awful. We wouldn't actually spend the $200/night (not including tax and parking) that the base rate was for this hotel on the weekend and probably won't return. For those of you considering it, the hotel is well maintained considering it was built in the 1940s and the staff was nice. As others have said, I recommend thoroughly evaluating the DC hotel scene before spending your money at the Average Hilton D.C.