I spoke to my Brother-In-Law who handles claims at a large Auto Insurer, as well as my Wife's Uncle, who is a supervisor at another VERY large multi line insurer.
This was like over a month ago, and I totally forgot about it until I read this thread again.
They both said there are shit loads of calls that come in regarding damage to cars from shopping carts. They rarely make a claim, as the Store isn't liable, and the person who put it there is usually long gone. But it clearly impacts precisely a shit ton of people. And due to the deductibles, they end up paying out of pocket to fix it, if they fix it at all.
I did ask them if any of those carts that damaged their policy holders' cars were in a Cart Corral. They thought I was joking, and looked at me funny, and promptly started drinking their beers again.