Actually given how kids are shut out of a lot of net commerce due to not being able to get a credit card and such, but may just have a decent graphics card for games and time and knowledge to figure things out, I bet the number that would do this is far more then you would suspect. It also is smart marketing to get kids used to bitcoins and the idea they have value.
Agreed. And bitcoins are a boon to anyone wanting to hide financial transactions - and for those reasons cannot use conventional payments online.