That spray is complete bullshit - Doesn't work. Didn't you watch that Mythbusters episode? To test, what you need to do is just take a camera with a flash and take a photo of your own license plate from a similar angle to what the speed camera would catch you at, you will find that the license plate is in focus.

I know someone who works at a company here in AZ called Redflex, who manufacture alot of the Photo Radar systems, including the fixed systems here in AZ on the Freeways and at Red Light Running cameras. The only people who don't get tickets are motorcyclists wearing helmets. If you are in a car, regardless of what kind of spray or cover you put over your license plate, unless it is completely obstructed, you are gonna get a ticket.

There is also a myth that if you register your car in your wifes name and her car in your name, if you get snapped you won't get a ticket. They will still send the ticket, hell - they will even pull a photo of your spouse from the DMV Licensing computer that they have access to at the processing center.