Hoboken is trying to reduce its car population by placing rentable cars right on the street. It's like Zipcar but uses on street parking. This is a good idea to reduce congestion; unfortunately it's really only possible in a truly urban neighborhood.
Me, I just wish I could get a Zipcar lot somewhere in my neighborhood. Phoenix's Zipcar program is based on the ASU campuses, but I think there's an untapped market in a denser neighborhood like mine.
NPR's Marketplace aired a story on whether it was cheaper to drive or use public transportation. Unfortunately, the story is very NY/NJ based and doesn't offer any broader guidelines. It's an individual and regional issue. I wish they had covered more general aspects on deciding if car or public transit is worth it for you.