Parking Day 2011, Vigo (Spain), according to http://www.quetipos.com/?p=58

Parking Day is an annual worldwide event where artists, designers and citizens transform metered parking spots into temporary public parks.  It is presented as an open source event. Conceived by Rebar, a San Francisco based design studio, its aim is to raise awareness about the amount of public space used by cars. The idea is simple: once you have paid in the parcmeter, you have a right to use the space for a given time, and it is only up to you to decide whether you want to use it to leave a car of other use.

In 2012 it was yesterday, 21 September. Since the first time in San Francisco, and according to the manual, metered parking has hosted wedding ceremonies, worm composting demos, public parks, free health care clinics, glass recycling, political campaigns,  public kiddie pools, and all sorts of uses. There is also a manifesto. In some american cities, as in Philadelphia, it is becoming a relevant movement.