I was visiting Reno, NV, a few years back and decided to visit a local gay bar that was listed in my guidebook. Driving in, I was struck by the number of pickups in the parking lot and figured that guys in Reno must be particularly butch. Turns out it was lesbian night at the bar. Oops.
Hands down, nothing screams queen like seeing a guy driving a VW Cabriolet. (That's a convertible to those who are homosexually challenged.) Mine personally is a 1987 Wolfsburg edition -- white with a white top and a white leather interior. Of course, it comes complete with a rainbow flag on the back.
In the same way that we gays drop too much cash for a pair of high-end loafers that aren't comfortable, we get cars that may look cool but don't necessarily make much sense. So I'd probably say the ultimate gay man's car is foreign, trendy, and sort of macho (making up for the floral-print duvet at home).
My nominee for the ultimate lesbian car? I'd say a pickup truck, like the Chevy S-10. It's rugged, functional, and affordable. It's tough enough for a lesbian. They won't get any flak for their "Hate is not a family value" bumper sticker in a vehicle like that.
Doing a quick survey of what all my gay friends drive tells me that practicality rules . . . mostly. Subaru Outbacks and Saturn sedans predominate, BUT hot German sports cars are also very popular. Nothing says I won't be spending $160,000 raising each kid more than a BMW Z3 roadster.