I used to buy the 30 day pass, and its a great deal, but I've lost one, and another has just gotten totally damaged. I keep the metrocard in my wallet nice, but its so flimsy it gets messed up like its nothing.
Now I just use the weekly pass. Costs a few more dollars per month, but its worth it cause in case you lose it, its not that bad of a loss.
One thing you can definitely say about the NYC subway though, is that you really really dont need a car to get around in the city. The subway will take you within a few blocks of anything. Having a car in the city is more trouble and hassle than its worth.
But queens is a different story. Buses are so sloooooooooooooow....