The biggest problems with the T are that it doesn't go everywhere and it shuts down early. But this is a much bigger problem for those of us who live in the area than the average tourist. Assuming that you stay in the city, most major attractions are easily accessible by the T, and close to everything else is accessible by bus. And if you're staying in the city, and are out late in the city, a cab ride at 2 or 3 or 4 in the morning (if you actually find a place open that late) is not likely to set you back more than $5 or so.
The biggest problems with the T are that it doesn't go everywhere and it shuts down early. But this is a much bigger problem for those of us who live in the area than the average tourist. Assuming that you stay in the city, most major attractions are easily accessible by the T, and close to everything else is accessible by bus. And if you're staying in the city, and are out late in the city, a cab ride at 2 or 3 or 4 in the morning (if you actually find a place open that late) is not likely to set you back more than $5 or so.