To answer a previous question about the Hancock Tower - the middle floors are dark because they were Hill Holiday's space.
Back when the 'Boston good old boys network' owned the building, Jack Connors got to keep his ad agency in prime, high-luxury offices at the Hancock Tower at a discount. Once the building traded hands and an NYC firm took over, they jacked up rents to the normal market level and Hill Holiday fled to more generic and cheaper space downtown.
My good friends are working on a re-positioning campaign for the Hancock Tower, I'll post some images once he gives me the approvals - there are some cool changes in the works over there. Some of which has been publicized and some of which has not.