More and more cities are discovering the value in low-cost experimental pilot projects for public spaces and streetscape redesigns. San Francisco is certainly among the forefront, but this is a global phenomenon; the recent Nørrebrogade street redesign here in Copenhagen (from a high volume automobile traffic artery to the most successful bicycle-oriented street in the world) began as a three month pilot project.
This approach is particularly well-suited to most local political structures - the projects are low cost and potentially temporary, so the barrier to experiment is low. If the project succeeds, the politicians win. If the project fails, the project is scrapped with little ramifications. No harm, no foul.
I expect to see this more and more.
San Francisco is Reclaiming Streets for Pedestrians and Cyclists, Creating New Public Spaces