I have read this this thread with interest and whilst I know plenty of parents and young people will be sensible about this game, to say that there is 'nothing to worry about' and “it’s good fun” and “I don’t see a problem”, isn’t strictly true.
I had a Sixth Form student (16 years old) get lost in Peckham two nights ago whilst playing Pokemon Go – the game had drained her phone battery and she got quite freaked out. (it may sound funny and odd in this day and age but her parents had no idea where she was and as she was so used to her smartphone, as most kids are these days, that she wasn’t sure what to do, so wondered around for a hour in the dark, which is quite scary to think about what could have happened to her).
There have also been plenty of reports of people falling over and grazing or cutting themselves because they're not paying attention to what's in front of them while they play. It’s dangerous to wander around distracted – how long till the first news report of a young person being run over because they were playing Pokemon Go on their phone and weren’t looking where they were going? (yes I know they can do this without playing Pokemon Go but the point of the game itself to watch your phone whilst walking doesn’t help)
One area of caution for parents of Pokémon GO players, is the part of the game where players can lure other players to specific places. There are reports of Pokémon destinations (called “Gyms” and “PokéStops”) appearing in people’s homes or schools, even near playgrounds and the BBC reported near ‘houses of ill repute’. Any game this popular that includes an intrinsic ability to lure young people (the game is rated for ages 9 and up) to unknown places should set alarm bells off with parents.
In addition, the game may create a false sense of camaraderie.
Like many of the new Internet-age video games, players can play with people they don’t know across town or around the world. Players can jump into a game with a room full of people they don’t know and shouldn’t trust. Pokémon GO adds to think where you might meet up with dozens of people at a local park for a battle or a very smart peadophile who manipulates the situation. I read of a news report that four people were arrested after they used the game to lure players to remote places and then rob them at gunpoint, in America. 
In response, the makers of Pokemon Go have said people should "play with friends when going to new or unfamiliar places" and "remember to be safe and alert at all times" but as it’s only just arrived in the UK, I am worried there may be ‘some’ parents (not all of you!!) who genuinely don’t know much about the game and therefore, some young people ‘may’ be at risk.
Lastly, on Android phones, people are downloading corrupted apk files within the game without a second thought, which puts their smartphone at risk.
I apologise for the long post but I do feel the above needed to be said!