The exit at my metro stop is aaaallll the way at one end of the platform, so on the way home most people going here ride in the last car. I know a ton of people who live around here, so whenever I get on the train, I look around for anyone I know. I decided I have to be proactive about it after the second time I happened to be caught without a book, had an especially deadly boring ride, then realized at the end that someone I knew and would have enjoyed chatting with was sitting right near me.
You'd be surprised how often I find someone - a few weeks ago I saw a hand waving when I got on and it belonged to my Norwegian dance sister (people assume we're sisters - apparently we look that much alike). She'd just gotten back from Norway and we had a grand old chat about our respective European vacations. Tonight I'd been sitting there for a while when I realized a woman sitting across from me used to give me rides home from this choir I used to be in (with Tall L). Her son is in the same high school program I was in and is about to go on the awesome 10th grade trip.
It's nice when I find people to make up for my failure to carry reading material. Although I'll admit I'm less happy when I run into people in the morning, when the metro is silent as the tomb, any talking is against the unwritten rules, and I personally would rather be sleeping.