I've always enjoyed intelligent, socio-political commentaries, particularly ones that are playful and displayed in unconventional places.
Yes, I do consider some forms of "Graffiti" art, and no, I don't consider "tagging" street art. There is a very important distinction to be made between Street Art and Graffiti.
Of course, people will gawk when Banksy's work has been painted over, but the basis of graffiti as a form of self-expression depends on it being temporal and fluid. We shouldn't morn the fact that Banksy's work
That's Street Art.