Fortunately, there's another bus that you can take to the Presidio -- it's free, it's comfortable (big soft comfy seats!) and it even runs on natural gas. It's called the "PresidiGo," and it's awesome.
One of the best things about the PresidiGo is that it adheres to schedules. Unlike Muni drivers, who time their runs according to their own own personal whims, The PresidiGo departs every half hour on the dot; and even though it has to contend with the same traffic as Muni, it's really reliable.
There are two routes; one loops around the inside of the Presidio, and it's free to everyone at all times. Another runs from the Presidio down to Embarcadero (rumor has it that it's about to expand down to Caltrain). That one's free to Presidio residents/employees during rush-hour, and to everyone else during the rest of the day. Or, if you have a Muni pass, you can ride it for free at any time.
We've ridden the PresidiGo a number of times, and it's always a delight. Now get out there and enjoy the lovely weather -- you don't have anything better to do today, do you? (Tip: call your mom to say hi.)