My golden retriever's been in my boxster three times in the four years I've owned the car.
Every single time, she's scratched the crap out of one or more items. The seat, the door sill plate, the center console, etc.
She goes absolutely everywhere with my wife and I (stores, work, friend's homes, etc.) but only in the Lexus' back seat... not the boxster.
I will say though that when she's sitting up in the seat with the top down and rests her head on the window sill (a trait all Goldens posses), everyone driving by can't take their eyes off her
If I had a smaller dog like Lovebunny, I'd probably take it in the car more often.
Securing a large dog in a car can be done and they make harnesses for your seat to protect the dog and keep it from jumping out:
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=639