Dewey, Cheetham, and Howe are located above the Curious George Goes to Wordsworth store in Harvard Square, Cambridge. As has been noted, their most famous "clients" are Click and Clack, of Cartalk. Most interesting about the Dewey, Cheetham, and Howe office window, though, is that its got a remote-controlled webcam mounted in it, facing Harvard Square.
One can click to enter the queue and eventually get 60 seconds to control the webcam, panning and zooming around the square. Want to watch the hot chicks at Abercrombie & Fitch? Go ahead. Rather look at the salami in the window of Cardullo's? You can do that, too. Plus, the lighting is pretty good at night and it's an interesting way to people-watch. It's in the time-wasting section of cartalk.com, if you're interested. If you see me there, and successfully click on me, you may be rewarded with a rude gesture. (gratuitously stolen from the Cartalk website)