I use two online social services: LinkedIn (en) and GoldenLine (pl). My activities there mostly include adding people I know or work with to my connection lists. I think it’s a good idea to keep such list of friends; you never know, when you need to contact somebody you knew in the past. Also, one beautiful day, you may get a contact from a head-hunter 
Recently, I’ve updated my profiles on both those services. You can view them:
(LinkedIn)
(GoldenLine)
