Orkut seemed to be a good timepass and nothing more. So, gave up that too even before.
Checked out LinkedIn - I find that quite useful. It is a professional forum. Some of the groups are very active and relevant. Not too much of junk postings there. You can ask questions and people respond sensibly.
Then checked out Facebook. I did not like the user interface. Its utility is also doubtful - except as a time pass. I also hear a lot about Facebook people's tactics on 'freedom control', copyright, etc. So, became quite inactive on FB too.
Twiiter is the latest I am trying, what with all the bollywood and big people all there. It is hard to follow too many people. But there are useful information coming there. Some relevant stories, news, updates, and some timepass.
But on landing here accidentally today, there are some ancient civilisations still here, and some occassional movements too. So may check out once in a while.