Yep I think we introduced lollies to Matilda with the car seat tantrums. I also remember holding Matilda in place while she howled & having people walk up to me in car parks and ask if I was okay.
Now things are less traumatic, we have the occasional tantrum but they are all about power, for instance if Matilda feels that she has no choice, she gets more upset. So I try to make her feel that she is making the choice to get in the seat and go. She gets to go to the park on the way etc etc... sometimes its food, sometimes its getting to do somethat that she loves. "Do you want to paint? Okay lets get in the car & go!" She often tries to sit in the passanger seat and gets cranky about having to sit in her car seat but I just wait... if she is bad and refuses I tell her either she gets in her seat or I put her there. That always works. What she hates more than having to get in the car seat is not having the option to get in the seat herself.