I had one scheduler recommend I "like" their page, and it's not a company I was signed up with. He was starting an invitation only page, and I thought it might be fun to talk with other shoppers. I signed up with the company and joined the group, but they have no shops in my area. The scheduler answered all my questions about availability in seconds, saying they have sent proposals to businesses in my area, so fingers crossed. I am still part of the group, and I did get to chat with some shoppers, which was really cool. I did deactivate posts from showing up in my inbox until they shop my area.
I've liked some survey companies and focus groups, which is great because they will post openings on FB and Twitter before emailing you. I've liked Customer Impact as well. I shy away from liking too many, preferring to keep things private. It is fun to see news from a preferred company to shop for, but I'm very selective. I think they are the only one I've "liked".
Social media can be great networking, I'd say join a closed group if you get invited and am interested, who knows what opportunities you will find.