Second Friends is the name of a pretty good Facebook group, primarily a place for Residents to promote content and events in Second Life, displayed in a near-real time stream. With nearly 1600 members, it's fairly large and busy, and could probably use some curating, to better expose really noteworthy events. This Facebook group and some others I've joined use life Facebook group chat, providing like Plurk another alternative to Second Life communications besides those offered in, well, Second Life itself.
What other SL-related Facebook groups do you recommend? Of course, New World Notes has a Facebook group of its own, which has hundreds of lovely people, but needs more updates (ahem.) And yes, Facebook does technically forbid accounts that are pseudonymous avatar names, but as a Facebook rep told me a couple years ago, the vast majority of the "fake" accounts which Facebook actually bans are reported by other users, not from active policing by the social network. Which probably explains why Facebook has so many accounts which are actually avatar names. (The official Second Life page has over 107,000 members, many or most or whom are avatars.)