I used to be on linkedin, but got tired of duplicating information that is already in my CV and on my website. Then linkedin has a way of nudging you towards filling in ever more stuff (previous employers et cetera), if I remember correctly perhaps even with some daft reward system. It has both free and paid-for services, and I very soon ran into the limits of the free service. Many of the establish-a-link e-mails I received felt tedious and some people like to farm links like, well, link farms. But first and foremost these days I wish to control my footprint on the web, especially regarding the type of information that linkedin requires. Hence I withdrew. It may well be that if I were unemployed or simply looking for another job linkedin could be useful. To me the uncertainty in the rewards and the cost of playing are too large.