I'm not going to begin to argue the artistic merits of graffiti (through definition it's art but to me it's ugly).
Graffiti takes all the rules of graphic design, colors, and message then throws them away. Now normally that would be hip cool and trendy but in this case all you wind up with is a logo/font/banner as illegible as the one on this site.
I respect what they are trying to do, promoting artists who have trouble getting recognized. By the very nature of graffiti art the artist comes up from local neighborhoods un like some of the rich kids art I've seen recently (kids who can right off the bat afford a studio and a gallery and the paint they use whilst living a comfortable life whether or not they sell anything). What I will never be convinced of is that graffiti is anything but vandalism when it's unwantedly place on your property. I guess its the nature of low class kids to think that you'll like what they like. Why else would they blast their car stereo or yell at each other from across the street? Although I could equate it to animals marking their territory and shouting out mating calls but that would be rude.
What we're going to see in the near future is local and federal policing agencies using the internet to track down crime, first major crime and then petty crime. In the end websites like this will not only be held liable for promoting criminal activity but also lead the police to the perpetrators (jeez, I feel like and old grandpa yelling, "get of my lawn, kids these days"). But since I've had to pay to paint over other peoples graffiti I'll be laughing when you start receiving citations in the mail brought on my photos you took and posted on the internet.