Re: LinkedIn
been using linkedin for 5 years, joined in 2004 so been on it for a while. I find it very useful, have been able to maintain old contacts, make new contacts, and have had career opportunities come my way through linkedin. my previous role in 2005 came from a recruiter finding me on linkedin, and same for my recent move.
There are other things aside from linkedin, jobfox, naymz, plaxo, twitter, visual cv
There is a good book called "Me 2.0" which i highly recommend especially for new grads and professionals, however it does have a good utility for people who have been in the field for sometime.
I would highly recommend, people show their portfolio of work at visual cv, their experience map on jobfox, profile and recommendations on linkedin for sure. and join industry groups on linkedin and be active..but when you have something valuable to add, build your reputation etc.
I will not say I am an expert on this stuff and you should read up articles o personal b*****ng. Lucid is a very good resource on GS as well. If i can be of any help to anyone who is just beginning on these, please do not hesitate to ask any questions.