One of the great benefits of the net for young people is that it exists and that writing, in some form, is back in fashion.
I remember when I was at university I used to write to my parents and friends quite frequently but it was soooo frustrating having to wait for a reply. Next came the stage when youngsters seemed to spend all day on the phone and in front of the TV and occasionally would send e-mails. Now my teenager daughter writes a lot with Messenger, Facebook, Twitter etc and now she has decided to start up her own blog on which she regularly posts articles in 3 different languages.
So, if the Harry Potter series got kids back to reading then social networks have got kids back to using writing as a form of communication. I'm confident that most of them can adapt their written language to their audience in the same way that their spoken language with their friends is different from with their grandparents.
I think alot comes down to the use of abbreviations and "gaming" language that also finds its way into real life.