My impression of the actual cupcake was similar to the rest of you; they're ok taste-wise, but not enough to make we wait on a line down the block. The chocolate / vanilla version I had was very pretty, decently moist and right-sized. But you can get similar (or better) goods without the hype at B&W or Furin's.
When I went on Sunday, they were clearly overwhelmed, but giving it a good shot. From what I could see, the kitchen was tiny. There were two people back there, one frosting and one running cupcakes to the front of the store.
I give it about 2 weeks until they dump the interminable process of folding an individual square of wax paper into thirds, wrapping it around each cupcake, and placing it slowly in a bag or box. Unnecessary and annoying as hell. They're not fine jewels.
According to the WaPo Food Section today, they originally intended to operate as a catering-only outfit, with the walk-in business being incidental. I wish them well and I hope they settle on a business model that works for them. It's a very cute store, so I suspect it will soon be publicized in every DC tourist guide.