Over the weekend the SFMTA tested out the E line in the first of two pilot runs. What is this E line, you ask? It's just the F, but rerouted so that it takes people from CalTrain all the way up the Embarcadero to Pier 39. It's designed to ferry Peninsula folk, who are of course natural yachting enthusiasts, to the America's Cup via historic streetcars, and it's going to be tested again in October when the World Series regatta races return to town.
The SFMTA is looking for feedback on the pilot program via their website, as LiveSoMa points out, and there may be a chance that streetcar line might be a permanent addition after the Cup if there appears to be greater demand for it. It seems useful, also, in getting people from the Ferry Building to AT&T Park during baseball season, and given the slowness of the Muni Metro in and around Embarcadero Station, would probably be a faster means of getting to a ballgame.