Facebook: One word/phrase to describe audience effect of it?

I notice in facebook and other social networking sites that people almost routinely access and view it, but seldom actually take part and interact. Isn't there a word or phrase used to describe this? Is it an audience effect? Is there a word used to describe the weariness of "commenting" on things because of what others may think of them? (Yet, again, they still routinely log in.)