Remember when someone older than you first got an email account? They probably sent you at least one joke, and it was likely to a long list of recipients. Actually, they probably sent a lot of jokes. There is a similar phenomenon with social media. While it may not be jokes, we are inundated with over-sharing of the same stuff.
First of all, there is a difference between sharing and making something public. Posting a social bookmark to a service like Delicious does not create additional noise for your networked peers in a social network. This is making your work public. But posting your latest collection of webpages in an activity stream is sharing. Doing it poorly adds more noise than signal.
Some interesting points about levels of openness and the etiquette of openness