I like the idea of Autoshare/Zip Cars, but the problem is they aren't cost effective if you're leaving the city, which i do quite often. Right now i'm renting cars which in the long run doesn't make sense.
When I lived in the city I used Autoshare exclusively for out of town trips. Driving in the city is dumb. I have a bike.
It's like $80/24h with 150kms included. 10¢ per km after that. That's 150kms/day, so if you take it out for a three day weekend, you can go 450kms before you have to pay extra.
Insurance alone on your own car is going to be at least 200/month. plus gas. plus insurance. plus maintenance. plus licensing. plus repairs. plus parking. plus plus plus.