Well, here is how it is for me.

I consider very many people online good friends, and I have a certian ammount of concern for my friends. The problem is that with many of the people I talk to the only way I have to contact them is either a chat service or e-mail. If they vanish from the face of the net for a week, a month, or longer, I have no way of knowing what has happened to them. Perhaps they lost their internet connection and are living life just fine, or perhaps they have come down with a horrible death.

One case to illustrate it. I had a friend I used to talk to all the time, then one day she vanished. About two months later her mother logged onto her e-mail and sent out an e-mail to everyone in the address book informing us of the fatal accident that my friend had encountered two months earlier.

So I tend to worry when my friends don't contact me at fairly regular intervals, and since I often have no other means of getting in touch with them (With my friends in the real world, even if I don't see them often I have ways to contact them or their family, so I can find out if they are alright a lot easier) to know what is up.