I was heading to San Francisco’s Chinatown for dinner last night. The easiest way from Union Square appeared to be to hop on the cable car and take it about a 15-20 blocks. Price for the ticket is $5 a piece or $10 for me and my fiancee.
The Boston T is about $1.25 a person, so you pay four times the price for the history of being on a cable car. We ended up taking a taxi on the way back to our hotel (twice the distance than to simply Union Sq.) and it costed us $7.80 (not including tip).
As an aside, if you ever find yourself in Chinatown in SF, stop by The House of Nan King. The first time I ate there, the owner ripped the menu from our hands and gave us the house special after asking our dietary restrictions. He brought out beef, chicken, and pork dishes. Everything was fantastic. Last night we ordered off the menu, but it was just as excellent. We recommend the beef w/veggies.