The calendar page on the San Francisco Opera website has an iCalendar link which I thought would be handy for importing their performance calendar into my Google Calendar. However, when I tried it, Google Calendar only created one event. There's a slight problem with the file, but after a bit of hacking, I came up with a fixed version. If anyone would like to give it a try, I've uploaded it here. For the tech-savvy, I've also made it available on github.