I never got on back in 2006 or so when it was really escalating in popularity, and I still haven't. I am not much of a follower or someone to "join" anything. Now, at 31, I have more formed and thought out reasons why it's not something I would participate in. Doubtless, it's a great tool for many people to connect with loved ones and family across the country and world, but what I see from most of my friends, and immediate social circle is just shameless posturing, curation of a life to look down on others, and prop themselves up below whomever the target is, and it encourages group think and a small world view.
Of course, I have the same impulse to share pictures, for whatever reasons, shallow or not, but I just keep the pictures on my phone, for me, and anyone interested enough in my personal life to see them. If I post pictures of me wearing Valentino in Paris, or shopping on Rodeo Drive, or checking into Hotel Martinez in Cannes, eating Michelin star in Mallorca, or San Francisco, material things, for sure, that also reflect successes and travel to me, what message am I sending to "friends" or people who look at my posts? For the ones for whom those are attainable, it's whatever, but what about my friends who can't do that? What about the ones with 2 kids working a "normal job"? Do I want to "stunt" on those less "fortunate" then me? Sometimes I do, for reasons of pettiness, and insecurity. But, that's not who I want to be. I feel half ashamed to LIVE it, much less throw it in someone's face. I should take the 600$ for a hotel, and split it between my friend's kids, or give it to charity, or make sure my friends from middle school who got years have money on the books.
Also, keeping a perspective, that I am merely at one level, and others are at a much higher level, that it makes it very foolish to brag, humbly or otherwise about these sort of things.