I hired a bicycle yesterday, and this morning — despite the weather still being rather sub-optimal — I decided to take it out for a spin. Turns out that this wasn't such a smart move. About 5 minutes into my first ride of San Francisco, I rode over a messy intersection of cable-car tracks in the road, and my bike simply toppled over. As a passer-by said to me, "when they get wet, those tracks are deadly, they turn into black ice". Fortunately, I wasn't going very fast at the time, and neither myself nor the bike were seriously injured. But I did get a bit of a flesh wound, on my left palm and my left knee (some of the usual suspects in bike prangs).
I made it back to the Green Tortoise with no problems (it was only 5 minutes away), and dressed up my minor battle wounds with some first aid supplies. The accident happened down on the Embarcadero, near the piers and the seafood shops.
Big warning, to myself and to anyone else who wants to try riding in San Francisco: beware of those tram tracks! They may look sweet and innocent, but they're not. It's best to ride over them in as close to a perpendicular angle as possible, and it's best to avoid riding over intersecting or splitting tracks altogether. If you have to ride over them (which you do, sooner or later, as they're everywhere), take it slow, and avoid getting your tyres "caught" in them.