Is greedy positive or negative?

Greed is roundly condemned by all the major religions. In the Christian tradition, greed, or avarice, is one of the seven deadly sins, a form of idolatry that forsakes things eternal for things temporal.

Many economists tend to believe that greed is good, claiming that greed is the driving force of economic development. The argument is that if people are eager to maximize their own interests and are never satisfied with their current possessions, they will eventually engage in activities that are beneficial to the whole society. The underlying logic of this proposition is that greed promotes individual performance, which in turn benefits the development of organizations and societies. However, there is a missing link regarding whether greed facilitates individual performance.

What do you think? How do you define 'greed' anyway?