This question is very similar to various reflections on "is using a groupon on a date a turn-off?"
In either case, there's a lot more contextual undercurrent that needs to be explored. Let's stick with the Zipcar example, though:
- Depending on where you live, owning a car may be a rarity, and thus there may be no expectation that a date will be picked up in one.
- It can be quite cool to be picked up in what is basically a "brand new" car, with all the latest features, and a cool remote entry system.
- If your date is "politically green", a Zipcar can be overtly attractive – so long as the use of a car is relevant to the date itinerary itself.
- If your date would write you off as cheap, or score you negatively for showing up in a Zipcar, I'd have a serious re-think about how great a match they are in the first place.
By and large, commoditized symbols of wealth like automobiles, watches, and Ed Hardy sunglasses speak to the lowest common denominators of attraction – financial security and the attendant access it provides to clubs/restaurants/other high end venues.
If you're just looking to score, you may well statistically be at a disadvantage for "scoring" compared to someone who purchased the same model car – but the variances from person to person, and the million other ways you can "blow it", especially with the shallow types who care a lot about what you drive, basically reduce the difference to mere background noise.
Try not to worry about it too much. If you can't escape anxiety over driving a rental (Zipcar or otherwise), then I would advise incorporating an exotic non-local accent and pretending to be from a far away country (which should both explain the Zipcar, and give them additional reasons to casually hookup with you).
(Photo from Student Exchange, © Disney, 1987)