As you may or may not know, the F line trams go along Market Street and then along the wharves, stopping at such useful tourist destinations as Fisherman's Wharf and Pier 39. It is often filled with a mix of tourists and locals. At the other end of the line, they stop in the Castro.
In addition, the fleet of trains come from all over the world. You never know when you will step onto one that came from Milan, or from Zurich, not to mention many cities in the US. To see a full list of the trains, click here. They even have a blog about the F line and trains in San Francisco, it's pretty cute.
Oh, and if you celebrate it, Happy Easter!