I sure haven't. I'm not sure what's going on with that. Seems to work for most people. I guess you've probably tried to unsub and resub? Do they show up in the car showroom from the main menu? If so, they're working. Sometimes it takes a while to find them. They're more rare than their stock counterparts.

Shot in the dark, but you're looking in the right-hand bottom corner at auctions for the names of the variations of each car, right?

Unsubbed and resubbed several times, checked in the showroom under the car models themselves as well as at the end of the listing where the new car models are displayed, can't seem to get it to work at all. I thought there might be an issue with the files themselves, nothing seems out of place.
What I haven't tried is uninstalling and reinstalling the game. I bought it within an hour of release so there might be patch issues causing the problem. It did just occur to me to run Steam not in admin mode. If it makes a difference I'll try to post that here.

Cool, let me know what you find out. I bought the game 5 minutes after it came out, and haven't had any problems. After the first patch, did you launch the game with Reset Settings when you hit play? Then go in to main menu, quit out, go back in and set up your settings again. Maybe it's the admin thing. Hope you get it working.

It's not the admin thing, and I didn't even think about resetting the settings. I'll give that a shot.
EDIT: Reset settings did nothing. I may as well just move the files, back up the entire folder and hope that will do the trick.

Hate that you're having bad luck. Well, hopefully that will work for ya.