I frequent the website and someone recently asked 'what constitutes an identity?'. I found this an interesting question because there are several ways to answer it ranging from philosophical to technical but there is also the flip side - how easy is it for someone to assume your identity?linkedin
Social networking sites like facebook and linkedin promote information sharing, you can list work and school experience as well as share interesting tidbits about yourself but I do have to wonder just how much of that information could be used for illegal or illicit gain? All it takes is someone determined to have the sites database and not only do you have all the information that's publicly available but you also have other restricted data (assuming that the data is not stored encrypted of course).
These sites have a lot to promote them, they are a great way of getting in touch with past colleagues and for making new contacts but in many ways they scare me with the amount of information people are happy to give away about themselves - The potential for social engineering attacks based on information contained in this sites must be huge.