I have noticed that there are two ways of saying that. When somebody bothers us and we are mad so we tell him that he should mind his own business and stop spending time with us bothering us.
And there is an other way, when we want to say to someone that he should feel bad because his life is empty and he is dealing with crap and that he has nothing important in it.
I have noticed that it is used more offten in the net and I can think only one reason : People who like computers are usually people that spend many hours in front of them. There are people that in some way after being so many hours in front of a screen kind of loose reality. Their life becomes the screen and the mouse. I think that is because there is much lonliness in this world after all. Sometimes it is in our hands to stop be lonely and sometimes it is not. Or at least we think so. So sometimes this expresion is used for people that spend many hours in front of a pc loosing some of the good things that life has to offer. I once told that expresion to a friend of mine but not in a bad way. It was said out of love and care because he refused to go out and have some fun, he was trying to find a girl from the net and generaly could not see people around him that loved him and cared about him and they were in flesh and blood right in front of him. So I told him "You should get a life" in a very calm and sweet way. In some cases I believe it is not important what you say but the way you say it. So he looked at me like he have not seen me for a long time and said "What did you say?" I repeated explaining to him that there is a whole wide world outside waiting for us. To cry, to laugh and live.
We talked for many hours and then we went for some drinks. I told my friend how much I have missed the times we have spend together and all that fun we had in the past (note : he was only a friend of mine for 11 years. Not a lover).
Eventually we had a great time this night. And we promised to repeat that next Saturday. And we did. Now he is getting married. And he found his girl not from the net <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />
I don't know if this huge post answers any of your questions Kiya. I hope it does (cause I had a hard time writing it) but in conclusion I think that these words sometimes mean good and sometimes mean bad. Like the most things in this life in order to keep balance.
Ok I know I am writing crap. Could someone please stop me?