I am a LATE ADOPTER.
All my friends jumped in on LJ, then MySpace, which are now rather 'toast' compared to Facebook, and then Tumblr comes along and now this.
I am going to wait 'til I retire, then look around and see whether anything has stood the test of time (like ASCII text sent as e-mails - that's still going after 20 years or more,) or what's new at THAT time.
Also, once I retire I will feel free to post my political views and other philosophical beliefs without the threat of being fired, or having to worry about what a future employer might think...