Is Facebook any good for people such as ourselves?
Yes and no.
Yes, in that it offers a convenient way to keep in touch with people. Also, if you have problems speaking to someone in person, wall posts and messages on FB are an easy way around that.
No, in that you're not really interacting with people. Messages and wall posts aren't a substitute for meeting and talking with friends. See below for more.
Does it ever leave people feeling desperately insecure?
Speaking for myself, yes. I look at what my friends are up to in terms of their social life, their jobs and their holidays, and I feel woefully inferior.
If you're not content with your own life, FB can make things worse. It's like being the loser on a gameshow where the presenter shows you what you could have won.
Recently, I was 'unfriended' - I wonder if that term was in use before FB

- by someone that I considered to be a friend. We work at the same place and have always got on well with each other (in and out of work).
I don't know what has happened, but I know that I'm upset. I can't help but feel that I've done something wrong. Part of me just wants to move, whereas another part of me is wondering why it happened.
Do you get comfort from interacting there, feel "liked"? Does it feel fake at times?
I don't think comfort is the right word. It's just nice to keep in touch, even if it's in small ways. At other times, it's just a convenient way to arrange a gathering of friends.
As to whether it feels fake, that's a hard one. I only have as friends people that I know i.e. people that I've met at least a few times and have spoken with on a number of occasions (and I feel that I know enough about them to like them).
I think that's important because I don't see the need to be associated with people who are merely acquaintances, or people that I only have a passing relationship with.
I don't think it's fake in the sense that people are insincere. I think it would be fake if you saw it as a substitute for actual socialising and networking.