Creating an effective game economy is hard no matter what sort of game is being created. The relationship between the economy and game flow cannot be understated.
Amit Mahajan from Zynga provides a good overview of economy and social interaction.
I haven’t used their tool yet, so I can’t comment on what it’s like to use it. You can access it here.
If you know of any other tools for designing an in-game economy please let me know!