That first Banksy artwork made me go; Whoa!
I used to work with removing grafitti, mainly because I got paid, and secondly because I got paid for it..
99% of the things I removed were simple tags.
I came across one proper artwork, and I simply had to remove it, painfull as it was. The owner of that wall was obviously not particularly impressed.
I don't have any pictures of it sadly, since I was'nt the one taking them - the police certainly has a copy though.