I am very curious about Facebook groups: did you find good ones? My experience with Facebook content has been total garbage and I'd like to know if my experience is just circumstantial.
(If you're into art, be sure to check out art and artist groups/pages. People wonder where Flickr went and it's right there, not Instagram.)
Keep in mind that some of these groups actively use their Files and Photos sections which can be like gold.
FB's participation model does incentivize things like simple brigading & passive-aggressive behavior, though (IMO), so it's also a good idea to get a feel for the quality of discourse and moderation before diving in if you are interested in participating rather than lurking.
It's really too bad the participation model has to be so static across the entire platform, because some of the groups are one or two customizations/tweaks away from being really epic with regard to community particpation. You could solve a lot of the social problems there with a more dynamic approach to the software design & provisioning.