Before I even click the link, I think I know what you´re talking about.
... And I was right. I love Banksy´s work. I´m a HUGE fan of graffiti- when it´s done well. An interesting picture is far more pleasing to the eye than a big old ugly white-washed wall. It´s even better when the graffiti MEANS something, like it does here. He´s not just spraying the wall to make a mess or be a prank, there´s a message behind it.
I´m loving all the graffiti here in Brasil- especially my city. I´m going to go around and take pictures of my favourites sometime. : )
But, I´m not advocating going out and spraying everything you see- I wish more citys would "hire" graffiti artists to decorate the city. It would spruce up the place tonnes and be cheaper than other methods...