Personally I love it. To me it's much less vandalism than most of the advertising that infects our public spaces. And related to that, Banksy on modern art:

"The thing I hate the most about advertising is that it attracts all the bright, creative and ambitious young people, leaving us mainly with the slow and self-obsessed to become our artists. Modern art is a disaster area. Never in the field of human history has so much been used by so many to say so little."