Yesterday, Jordan Seiler (a GOOD 100 honoree) and a small army of artists took to New York's streets to replace what they contend are illegal billboards with art. Unurth has a great series of photos. According to The New York Times the city isn't providing much clarity about whether the billboards are, in fact, illegal, and some advertisers showed up to paste right over the art as soon as it went up. Hopefully the art prevails.