The parking garage at our airport has a system similar to this. It's not quite so sophisticated in that it simply lights a green light for open and a red light for occupied, but it cuts down on parking stress considerably.
It is essential to get the bugs get out first. Few things are more annoying than glitchy technology forbidding actions (cannot park there) which obviously should be allowed (parking places all open) because of a "computer error". There may also need to be an override / reset option.
Larry M. I agree with you. In fact, I wonder if SmartCars use this type of technology. I was at the SXSW Interactive portion of the festival in Austin, TX earlier this year and experience an issue where the smartcars we located using their smartphone app detected cars that either weren't physically there, or cars that were there had broken sensors so they were not visible on the app. We walked around quite a bit trying to locate the right Car2go. It would've been faster altogether not to even use the app.
I'm just glad that this type of technology has been developed and will be tested. I'm hoping they will do beta testing in cities all around the world and that cities will be able to budget well enough to invest in citizen-friendly like this.
So I get to the "open" space and find a Corvette parked there (not enough metal to trip the sensor). Or someone who lives there throws a chunk of metal there to reserve a spot in front of their house. This may turn out to be a good idea, but it will also have problems.