The folks at ifoAppleStore have a live webcam pointed towards the construction, and Flickr user kokernutz has posted a shot of the shrouded logo.
This store is on Boylston Street, directly across the street from The Prudential Center in Boston's upscale Back Bay. This will be the ninth store in the Commonwealth of Massachusetts and the first in Beantown. It's been suggested that it will open in May. I'll be there!