San Francisco is a really cool city for bikes. There are lots of bike lanes, lots of pretty sights to see, and the weather is generally never too hot and never too cold to bike. I've written about our tandem that my grandmother gave us for our wedding that we ride around the Mission and the Castro (as long as we don't leave our neighborhood, we can avoid the hills!). I loved seeing this graphic representation of San Francisco neighborhoods based on what bikes you'll see there. I think it's pretty true to life - my personal bike is a mix between Mission and Presidio, and our tandem is probably the only tandem you'll see in the Mission (I guess the rest are in the Marina?).