I have some old San Francisco Municipal Railway tokens. Are they still accepted as fares?
Yes, Muni tokens are still valid on SF Muni buses and trams as of February 2013. When boarding a bus or a streetcar, put a token in the cash farebox and get your proof of payment from the driver. In the Market Street tunnel, you can use a token to purchase a single ticket from the vending machines. You cannot use tokens to load a Clipper card (even a Muni-only one), purchase a return ticket, ride on a cable car, or ride buses and trains from other agencies in the area.
Younger people in the area may not have heard of tokens. Tokens are no longer sold (the Clipper card is encouraged instead) and are becoming a collector item.