Facebook - good or bad

I have been a member of facebook for just a few days but I am having doubts already.
Is it a valuable use of time to learn how to be a part of this online community when I could be spending the time participating in real people communities instead?
To me the word friend seems to be devalued when it is used so freely and without any depth. (My definition of friendship is summed up in the anonymous quote which I paraphrase "An acquaintance is someone I may spend a lot of time with, laughing and enjoying stories but a friend is someone I choose to cry with.")
So I am undecided about my involvement in facebook.
(If you are an uncritical fan read Janet Street Porter's article "Why I hate facebook". I would probably not go as far as her in her dislike of all social networking sites. See http://www.dailymail.co.uk/news/article-1138445/Janet-Street-Porter-Why-I-hate-Facebook.html )
On the plus side I can see the value of sharing photos and social invitations with people that you share these things with anyway. It is a good way to make contact with people that you have lost touch with. (Memory can be very selective - do I really share anything with the people who are the same age and once sat in the same school classroom except that memory?!) It is also a great way for discoveries (such as new quotations) or moments of serendipity to be shared.
Perhaps its greatest benefit is for people who live alone and don't have any other channel for interacting with people on the trivia of everyday life?
On the negative side it can function as a community in itself divorced from reality where so called friends may be not who the profile says they are. And let us be realistic about the trivia that is written on walls and the rarity of real wisdom.
I think I will stay with facebook as a tool for keeping in touch with folks I know and want to share with regularly. BUT I must be on my guard never to regard it as anything more than a tool or utility. It is useful but not indispensable. And God help me if "screen based reality" ever seems to be taking over from life as it is to be lived and enjoyed in the company of others....