http://www.youtube.com/watch?v=oUkiyBVytRQ
http://www.youtube.com/watch?v=IORuR5iRuxs
I've heard that the NYPD is even going after people practicing parkour now, though I haven't seen it on youtube yet.
(Full disclosure: I got picked up during one of these incidents. The judge dismissed all charges after the cop lied and I showed videotape proving it.)