I may not be one one of the internet superstars with a huge social media presence, but I do follow a fair number of people on twitter and google+. One of the challenges of the social media is when do you unfollow/defriend/uncircle. I try not to unfollow very often. There are three things that will eventually get me to separate from our virtual relationship.
Your political opinions sound stupid online
If you tweet constantly about politics. I pride myself on being open to new ideas but at some point the effort in not calling you an idiot becomes to great. If you agree with me politically tweet all the lame memes and blog posts you want :)
You whine all the time
This harkens back to my empathy post. Yes you are going through some bad times but eventually I just don't care anymore. The 40th time a blogger whines about their life, the life they created, I unfollow.
If you consistently use vulgarity, post nsfw stuff, or post hateful things. I followed one person who in response to an incident posted a series of very hateful insulting tweets against a group of people. I tried to just let it go since the person was obviously very emotional about the situation. But three days later they were still tweeting for people to kill themselves.
The google+ advantage
This is one great advantage google+ has over other social media. You can have people in a circle that you never see. They will still show up as followed but you will never see their inane posts. I admit my biggest google+ circle is of people I don't ever see.