L.a. Mta
I once rode the trains all the way from Hollywood to Long Beach. Went to some used bookstores, then came back. It took an entire afternoon--several hours. But it was interesting.
Actually, the train lines are pretty good for tourists. You can stay downtown, take the train to the walk of stars, and to Universal Studios, and not have to screw with car rental and parking hassles. But it's definitely not for people in a hurry, simply because of the vast distances to be covered.