This place served me one of the two best meals I had in Pittsburgh where I recently spent a week. (The other best meal was had a Max's Alleghany Tavern.) S&D is a little deli/grocery store in the District, so it's an interesting place to walk. Lots of shops and street sellers to browse.
We ordered periogi, haluski and stuffed cabbage. It was just to die for - rich and flavorful. I do not think you could have a better Polish lunch than we had. I would have it again in a heartbeat and I'll be coming back when I return to Pittsburgh.
There are interesting Polish products to buy at this store, too.