I used to do graffitis before starting college, painted for almost 4 years and was actually quite good but when I finished school I started investing my money in better and important things than montana's ;P
I remember doing a project about this exact topic when I was in senior year: Will kinda sumarize but I think graffitis are vandalism when they are done on buildings, they are appreciated as art when they are on legal places like abandoned factories and places like that. If you paint graffitis you should know that the #1 rule is that you should never paint on people's houses.
Here are some pics of when I used to paint (got 500+ pics on my facebook lol):
and can keep going for a lot longer lol