I smoke in my car just about everyday, rain or shine. Just like at home, don't care it it's hot or snowing, I'll be out there at least once a day to get my cigar on.
My drive to work is usually under 30 min, so most car smoking is a pipe. I will smoke a cigar on longer trips, no problem.
I leave as many windows down as possible, and never run the AC at all when smoking.
Luckily my wife doesn't mind, so on the occasions I drive her car, I may smoke. When I was out in CO last month, I smoked in the rental with windows down and no problem.