Leon Babauta has a great post on Zen Habits about all the lessons he feels he and his kids are learning from not having a car and riding mass transit. We use bikes a lot more than the T these days, but I like riding the T for all the reasons that he lists (and also don't like riding the T for some of the reasons that he lists--which shows the strength of learning to turn negatives into positives).
Sometimes I'm surprised by all the places that we can get to by mass transit, too. Noah and I took the blue line to Wonderland the other day, as I was doing some research for a production of one of my plays. We wore our swimsuits and went swimming at the beach there. We've lived in Boston for 11 years and never bothered to try taking the subway to the beach (admittedly not the world's nicest beach, but it's really not bad). It was a lot easier, cheaper, and faster than getting there by car.
I keep saying that I'm going to take him by commuter train up to Rockport, which is a town that I adore, and we can try bringing our bikes on the bike car. This summer, I really need to make that happen. With the commuter rail, we can access a lot of Eastern Massachusetts and Rhode Island, from Providence to Lowell, and all the way out to Fitchburg and Worcester.