When I first saw the work of Banksy I thought it was mildly witty, inoffensive though kinda conservative, it might have been where it wasn't supposed to be but it couldn't be classed as grafitti. He was out on his own, Banksy made people smile.
So what has happened as a result of Banksy's stuff? Well now every dickhead middle class art undergradute, wannabe Hoxton Hero* are out spraying the walls with the worst kind of grafitti and calling it street art, They even have a name 'smearkats'.
Thanks Banksy
*Area of East London which attracted artists due to low rents, now overcrowded with tossers looking for the bohemian lifestyle on a goldcard. A Hoxton Hero is someone who has little talent or imagination but by copying or tweaking other artists ideas try to pass it off as originality (whatever that is). A particular problem with conceptual art.