Wow - Great suggestions. I live here and would suggest the following:
1. Yep - do Alcatraz. It is fun, cheap and everyone wears head phones anyways so you are all on your own.
2. Walk through the Ferry Building, particularly on a Saturday morning/afternoon and enjoy the Farmer's Market. Go all the way in back and have a coffee at Peet's. If you are hungry - go find the place that serves great clam chowder and seafood salads. Everyone sits at the counter bar so it is ideal for singles. It is in the back of one of the big stores that has produce and a meat case.
3. Shop till you drop at the New Bloomingdale's complete with great food court underneath.
4. Haven't done it yet but everyone LOVES the walking tour: I Ate My Way Through China Town! Supposedly it is a blast. Book before you go.
5. Do a museum tour. We have several good one's downtown - San Francisco Museum of Modern Art.
Now somewhere you can get a visitors pass that includes the museums and other events.
6. If you like baseball and are here when they start, you won't feel funny being a single at the Giant's game. especially if it is midday - lots of people skip work.
7. Have a meal at the Tadich Grill on California Street near the Embarcadero. Once again, they have a huge counter where tons of people eat as singles. They are a traditional seafood house. Wonderful
8. Ride the cable cars

Oh and believe it or not Alcatraz sells out! So book in advance on line. It used to be the Blue and Gold Ferry line.
Also - one of the best things to do is to see Beach Blanket Babylon at Club Fugazzi in North Beach - Just silly fun! Now I would do this as a single but some wouldn't. The place is really crowded and if you sit up in the tier seats no one would even know you were by yourself.

Hi - I live in San Francisco and wanted to address your post. It really depends on what you like to do. If you're ok with having a nice dinner alone, then I would definitely go to North Beach for a good meal and people watching. North Beach is my favorite area - This web site has all the goings on in North Beach http://www.sfnorthbeach.org/


If you like art, then I would also hit the SF MOMA http://www.sfmoma.org/ or the De Young http://www.deyoungmuseum.org/deyoung/index.asp

The De Young might be more fun because it's in Golden Gate park, which has the beautiful Japanese Tea Gardens http://www.holymtn.com/garden/Galler...teagarden.html

Just be aware that the De Young is also close to Haight Ashbury (if you like the grungy scene and music, Amoeba records has the best selection of used music anywhere). Just be VERY aware of your surroundings in the park, and in the Haight, as it can be a bit seedy in parts. I wouldn't go there at night alone, but it's ok during the day.

If you want a nice museum with a spectacular view, then see the Legion of Honor http://www.thinker.org/

If you like great outdoors walks, then I would walk along Fort Mason through Marina Green to Crissy Field and up to the the Golden Gate Bridge. This is a very safe area. I go running here every day.
http://www.bahiker.com/sfhikes/crissy.html

One thing that I've found that's helpful is our public muni bus web site. You can plan your trips via buses, and you can see the most popular destinations. I literally take the bus everywhere.

Here's the web site:

http://transit.511.org/tripplanner/index.asp

http://transit.511.org/destinations/index.asp

Have a great time!

When I'm alone in a city by myself (I'm female) I like to go to theatre. SF has a same-day half price booth at Union Square, but you can sign up for free at www.goldstarevents.com before you leave home and check out plays/concerts that can buy buy in advance. There is a modest service charge. I've used them in Los Angeles ad they are extremely reliable.

The website for 1/2 price in advance in SF is www.theatrebayarea.org