Social Networks and Relationships....Why don't they mix!!

I asked this exact question on twitter and the first response I received was "Oil and Water"....BUT WHY?!If trust exists in your relationship then a social networking site should not present any problem at all. We hear all too often that trust is necessary, but really, it is the foundation to all relationships. You can't go around anticipating a heartbreak because really it will drive you crazy. The only thing that social networks do is bring more people into your life. If you're not secure with you're one person then that can mean death, and I can see how a social network could scare you....What do you all think?!