I would suggest that you put together a brief itemized list of the features you're planning on implementing for the site, such as the realtime activism map you mentioned. This may help you get more participation in general.
As far as the 21st goes, that's really soon... And I wouldn't count on the 12-21-12 vibe doing anything to make your site go viral. What you really need is for it to offer features and functions that are unique, helpful and enlightening. You sound like you're pushing in the right direction, but in my experience (I run a number of online ventures) mostly it's a game of inches, so don't get discouraged if it takes a minute to get established.
With any luck, though, it should be a good looking site.