Facebook Link of a Registered User

Patrick,
Yes, you can store their link in a Community Builder field:
1) Make sure you've enabled the Social Profiles - Community Builder plugin.
2) In Community Builder, create a field to store their Facebook profile link
3) In the JFBConnect -> Profiles area, create a mapping between the CB Profile Link field and the "User - Profile Link" in the Facebook dropdown area.

I hope that helps, but if you have any more questions, just let me know.

Thanks,
Alex