I have a few friends on FB. I'm not there a lot.
It annoys me that recently FB keeps asking for my mobile number, to enhance security. Why would I be more secure if they know my phone-number?
Don't know if FB is doing this too, but a online community like Hyves now offers the option to send postcards to someone. So, someone that has found you on Hyves, can send you real mail, without knowing your address, that information will stay at Hyves.
I don't know if I would be happy with mail like that. Think I wouldn't. Would come across as somewhat stalkerish.