Quick! I call urban planning/development online flash mob meme!
OK, it's not quite like that, but two websites make a trend, so on that basis, I reckon the emergence in the last few days of Co-Create London and Make London Better (allied with the 'where did that come from?' success of Secret London) suggests that location-based social media might not stick to the definition most thinkers had penned for it.
I am intrigued by the fact that online tools are being used so freely to try and impact the offline world. Another lesson: digital nativism means nothing unless it can be translated into analogue power.