See this thread:
http://www.flyertalk.com/forum/new-e...n-what-do.html
I had a 5 hour layover in BOS back in late February.
"I was in Boston last Saturday. Had plenty of time for some shopping, sightseeing, eating and even a trip to the New England Aquarium.
The flight arrived just before 7:50am, and I was downtown before 8:20am. Nothing was open at that hour, so I walked around for a bit and went through Boston Common. Did some shopping as I made my way back up to the New England Aquarium. I spent about 45mins in there. Then I grabbed something to eat in Sel de la Terre just around the corner from the aquarium. I started my return to BOS at around 12:45pm and was in the BOS AA Admirals Club at 1:25pm.
One of the most enjoyable layovers I've ever had!"