LinkedIn obviously fulfilled a pressing need in the social media world. The habits of individual users on Facebook have long been at odds with the exigencies of professional networking, giving rise to the need for a stand-alone work and professional social network. Given this, I believe that LinkedIn's valuation will continue to grow for the foreseeable future.
LinkedIn has become an essential tool for almost every working person. Businesses use it to find employees, and workers use it to job search. As long as it is successful it will continue to grow as more people start using it, while most of it's established users do not leave.
Much like Facebook, everyone in the business world has to use LinkedIn. Perhaps more importantly, a level of advertising is acceptable on LinkedIn by users, as it is considered a business site. This could allow for additional monetization of LinkedIn information, and should allow it to continue to grow and be profitable.
I have never been very fond of LinkedIn therefore I do not agree with this debate. Linkedin is mostly for businesses and not for the public, I think that facebook and twitter and instagram will continue to grow bigger but Linkedin will not. I dont know it is just my personal opinion.