Fans of Banksy Graffiti are in a strange position. If you don't live in London or any of the various International Cities where he paints his works, you're not likely to see them.
Even if you do happen to live in the City, you have to be quick or by the time you reach a new piece of Banksy art, it is more often than not covered in Plexiglas or has been chipped away and flogged on eBay.
Whilst it's understandable, if not mercenary, for people to be removing Banksy Art, I take more exception with those who chase their fifteen seconds of fame by defacing his stencils.
A recent example of this was a piece of Banksy Graffiti that he painted in New Orleans to commemorate the devastation of Hurricane Katrina (and perhaps a timely reminder of the lack of response from the Government just before the national election!).
One of the stencils was of a boy swinging on a lifesaver and this has now been blotted out with red paint. You could perhaps understand a kid doing this, but given the placement and height of the Graffiti, it would seem to be someone more 'mature'. I suppose by defacing a piece of art, they know it will be reported and ergo they have their little piece of infamy.