I don't really love the rules, as such -- I don't really want to be limited to playing stickball with loaves of sourdough through the streets of San Francisco -- but if the rules were loosened up a bit to let people do the coolest (...legal?!) things they can think of, or at least compete against others in certain categories (art, music, performance art, culture jamming, etc.) and share photos, video, audio, etc. it would be a really great way of encouraging cities to be the kind of cool, quirky places we'd like them to be. Hell, maybe you can even find a way to offer financial incentives for pulling off the best coups -- tip jars, etc.
Imagine a website where musicians, artists, culture jammers, etc. competed with each other to pull off the latest, best, most outrageous things in the real world. Sounds inevitable, really... I just hope it won't be completely MTV/Jackassified anytime soon.
Sounds like a neat idea for a site. Now all I need is a team of pranksters to help build it.