At least here in Sydney, the problem with the commons is that we have an unofficial rule that if you can walk away from it, it's a good parking manouvre. So especially in residential areas footpaths, intersections, parks, you name it, are all commonly parked on. It makes walking less easy than it might otherwise be. The interim period between subsidised parking and a market solution would probably see the usurption of any accessible space for parking, as motorists exeercise their "right" to park close to their destination. Not to mention the rise of "paking rage" casualties.

I also made one local council change their rules, as they failed to notice that my "X number of off-street vehicle parks" were sized to take bicycles not cars. They worked it out when they finally saw them on the ground and had a hissy fit, but it was a bit late as they accurately reflected the plans :) Now the rule says "motor vehicle" and gives a minimum size.