My daughter is 14, she said she has played it here and there. I have NEVER seen her on it at all. Instagram, Twitter, and some other site (that I can't think of right now- maybe Tumblr?) are where she is mostly. My two best friends' kids 9,8, and 6 are addicted, the 5 and 4 year olds are not into it yet (they are sisters of the 9 year old). Any time we get together, this is all they do- at restaurants, parties, no matter where we are. The nine year old hat a FIT when we were in a place where she couldn't get wifi (not sure why you need it, but I guess she did).
The parents of the 8 and 6 year old think it's cute. They keep saying "this is the new play date". I feel like the 6 year old is already socially awkward, and way too young for this (but is very big on doing everything his big brother does). They do other things, thankfully (mom throws them into every sport imaginable), but to me, it seems a bit excessive. The reason I worry is because I see how excessive kids are with the net as they get older (adults as well, obviously).
I believe that with all behaviors, everyone has a different personality; children and adults alike. For example, if I decide to have some Oreo cookies, and I take the entire package out and have it in front of me, I can stop at 2 or three. My daughter and my husband cannot. When she was little, if there was a huge spread of dessert at a holiday occasion, she felt it was okay to just keep going. The same with television, internet, staying up late on weekends and vacations, and any other thing she enjoys. This is not a new teen-age behavior. She NEEDS limits. I do not consider myself very strict with her, I try very hard (especially at age 14) to discuss 'doing the right thing'. I go to bed very early; I tell her "I am a grown up, my mom does not set my bed time, yet I still choose on some nights to go to sleep at 9:30. I pick my battles.
I also do agree that too much regulation and limits can bite you in the butt later on. Another friend of mine (with a 13 year old) is painfully strict with her. As strict as she has been with her, she too, would want to devour the dessert table if given the chance. My daughter tells me about the 'little' rebellious things she sees her doing. Right now, they are little things, but very soon, they will both be entering the world of High School, where their ability to self-regulate will be tested daily, in many ways.
Some kids need more limits than others. Some kids can be told "ok honey, no more Minecraft for today", others will pitch a full-on fit. Same with adults.