My mom and I did the trolley tour on a cold, rainy November day. We were so thankful to be able to hop on and off the trolley - not only to rest our feet and get dry and warm, but to get a sense of the city and its rich history from the local tour guides! The guides were entertaining and informative, and they gave us ideas for how to plan our stops and where to go to eat. It was expensive ($41/each) but worth it. Boston is walkable, but it's made difficult when it's damp-cold and with its cobblestone and uneven streets.
The tour runs from approximately 9:30 AM to 5 PM. We bought our tickets outside the Long Wharf hotel. We got off at the USS Constitution (a must see) and Charlestown (the Warren House is one of the oldest pubs in Boston), the North End (try Mike's Pastry), and Boston Common/Beacon's HIll. We never waited longer than 10 minutes for a trolley. A great way to see the city if you're only in town for a couple nights.