In a nutshell, the California Supreme Court voted not to overturn a 2008 voter referendum that amended the California Constitution to outlaw same-sex marriage. The ruling has led to an amazingly swift response by opponents of the decision, centered around Day of Decision, an event that intends to rally thousands of people in over 100 cities to demonstrate their support of gay marriage.
And to accomplish their goal, organizers have turned to social media, Facebook, and a wiki to coordinate their efforts.
The Day of Decision protest organization centers around a Wetpaint wiki. On this wiki, volunteers have put together information for rallies in cities in nearly every state, detailing the who, when, and where of rallies and candlelight vigils that have occurred or will occur today (Examples: San Francisco, Chicago). The Wetpaint wiki also has a vibrant discussion and an array of photos, literature, and videos available to those interested.
YouTube video, created by the Day of Decision organizers
While Wetpaint may be the organizational center, Facebook is proving the main method of spreading awareness. There are dozens of Facebook events (examples: Stanford, San Francisco, New York). San Francisco alone has 1300+ confirmed guests attending a rally later today. And finally, the Day of Decision movement has a Twitter account as well.