it's unfortunate, but to be honest there is really nothing you could do. As others have said maybe if your dropbox tries to sync, or mobileme, or if you know the mac address/serial number of the mb maybe if the thief connected the computer to a network you would be able to track the IP address. Pretty long shot, but maybe worth the try. Otherwise start saving for a new one, maybe invest in a kensington lock next time and add some software ahead of time to help if it happens again. Nothing will make your macbook un stealable, but if you have software, etc. it can make it more probable that you will get your device back.
while the firmware password can help there is nothing stopping the thief from just yanking the hard drive all together and buying a copy of snow leopard for $29 ...