The moment I purchased my first Magellan 360 GPS in 2004, I was warned to purchase an additional dashboard mount for it as California laws disallowed any objects to be placed on the windshield.
Come Jan 2009, this ban will be lifted and drivers in California can now put windshield mounted GPSes on their autos! Governor Arnold Schwarzenegger has re-legalized the use of windshield-mounted GPS systems in California. The new law also says that the lower left or right areas of the windshield are the allowable areas, so you should still use caution while doing mounting yours!
In all the years I spent driving in California, I have always mounted my GPS on the dashboard, so starting 2009 it will be exciting to see how the GPS units feel when they are windshield mounted! I remember using my first GPS on a Hertz rental car. It was quite conveniently placed in a cradle near the dashboard. Perhaps the windshield will be better!
Now lets look at the down side. Will the windshield mount really distract the driver from his/her view? That was the reason the law existed in the first place! Safety or convenience? What do you think?