As useful as you make it
I've been on LinkedIn for a few years, and many of the discussions I have read or participated in have been informative and, for the most part, professional. I have not endorsed anyone, and don't really care about the endorsements others have made concerning my skills. I much preferred the "expert" points one received by providing the best answer to someone's question -- alas, LinkedIn removed that feature last month. But since my professional interests span a number of fields, LinkedIn provides me with one site to discuss finance, technology, risk management, manufacturing, quality, etc. I just use it when I want information, share what I feel appropriate, and ignore the rest. Not unlike what I do with television commercials...
