Who is your "friend"?

Without any doubt - Facebook became a part of the Generation Y´s life (Gen Y - ppl in their twenties and thirties)
The other day I have been wondering about the Facebook ethics. I have not found any formal document regarding this issue. Anyone knows, if there is any?
My point is that people are using something, that they really don´t know how to use. Some people are more conservative with putting their personal info online, the other change their status every second hour to let me know that they have just gone to take a shower.

But the basic question I have been thinking of is following: Who to add into your Facebook account? The current number of my "friends" list is now (after a recent adjustment) 287 people. However, some of them are very close, some of them I have talked to just once or twice. The second group I try to reduce (nice to be in touch, but email is just nice tool of communication). And when it comes to adding people to your "friends" list, what is right? Who you should add and who is ment to stay out of your cyber life?

Facebook has its "Life cycle"(taken from a marketing perspective). The theory is elaborating on 4 phases - Introduction, Growth, Maturity and Decline.
The first two phases come together. The new user of Facebook is excited and keeps on adding new friends, interacts, puts all the pictures he has from now and from the past. The Maturity phase follows, while the user realizes that he is already wondering who to add and who to ignore (esp. the completely unknown stalkers) and starts to reduce the status updating frequency and pictures-of-every-day-life uploading. Accodring to myself, the Decline phase = the "reaching the know-how" how to use Facebook comes last. I think I am on the way there... :) Nowadays I choose who I know enough to add him into my cyber life page and which pictures and situations I want to share with all my "friends". As I mentioned above, the list of my "friends" has reached quite a high number. So, my question is - to delete or not to delete. And if so, who to delete. What is the measure of being a "friend" on Facebook. And here we come back to the beginning - Where is the written ethics of Facebook?