In the following video, Motley Fool tech and telecom analyst Eric Bleeker gives us three reasons to buy LinkedIn (LNKD.DL). He tells us how, while mobile has been a big challenge for other social networks because of the losses in advertising revenue, LinkedIn's business model of offering premium services benefits dramatically from the increased connectivity. He also tells us just how well LinkedIn is growing those premium services, and why the company has a solid moat even against other social-networking giants.