There should be something on everyone's profile or settings that they can chose to appear offline... like if you're online and you don't want someone to know.

Question

anonymous · Answer

Like skype...

anonymous · Answer

Exactly.

austinl · Answer

It is an interesting idea, however, the point of this site is to be social and ask for help or give help. It will be incredibly obvious that you are online if you posted a question "moments ago". Additionally, it would make helpers like myself not want to answer your question if you are listed as offline.
If you do not want contact with a particular individual, you can simply block them if they are an issue.
Just my thoughts.

xmoses1 · Answer

I know what you mean. and sometimes i wonder the same thing. I want some people to leave me alone but I don't want to sound rude by telling the to go away. I feel obligated to help them, but I don't want to send them away without any answer... idk does that make sense?