I have been using linkedin now for about more than a year ago and its a very good way of staying in contacts with employees and information of other companies
linkedIn is a useful way to keep in touch with colleagues and professional contacts, international companies, where contacts live overseas.
It also allows you to avoid mixing "business" network with "family and friends" network(on say Facebook) - your linked in profile should be relatively conservative.I only use free service of linkedin, I’ve never needed to upgrade to the paid edition.