I think of LinkedIn as the place you go when looking for a job, or in my case, for potential consulting clients or partners. My experience has been disappointing.
I keep hearing from those in communications and marketing that LinkedIn can be very valuable for getting the word out about an individual's or company's products or services. I believe these people, but I do think some industries/communities "do better" on some social platforms than others. And, I for one haven't found much compelling about LinkedIn for the geospatial practitioner.