Having been the victim of a cloning of one of our vans, and the huge amount of hassle, time and paperwork to sort it all out, I for one would now be very wary of posting my full reg on the internet. Having said that, they probably just saw it parked up. I also dislike google earth showing burglars a good escape route from my house and google street for showing them close ups of my security or lack of. I'm also paranoid that my son is telling all his "new friends" on facebook when we are in or not.
It's the world we live in unfortunately.