According to the estimable Sunny Hundal over on Pickled Politics, Facebook (the social networking site that's seen as cool and well tooled up, now that MySpace is creaking a bit - unless you are a musician) has significant potential for getting people to think and mobilise. It certainly is impressively constructed. Ekklesia now has a page. And on a personal note, so do I. You have to register to see them, but it's worth it. (Actually, my public interface is available. I have discovered that it is to be found here)
When you have set up your own Facebook page, which is very simple to do, the system will automatically search your email address book (if you allow it to) to discover who else you know is already on the site, so that you can add them as 'friends'. There are numerous features you can add, from a 'message wall' to books to maps, as well as various groups and causes. Not that I'm advocating relocating your life online, but I have found it a useful way to link with other media people and to look up some people with common interests.