The green building market is estimated to be worth $30-$40 billion annually by the year 2010. By 2010, approximately 10% of commercial construction starts are projected to be green. According to a 2006 McGraw-Hill Smart Market report, every business day, $464 million worth of construction registers with LEED.–Wikipedia

“The new 8,500-square-foot facility was designed to achieve the highest level of ‘green’ building certification by the U.S. Green Building Council - LEED Platinum Certification. …Guests learn how to implement sustainable features in their own homes and businesses.”–The Environmental Nature Center (ENC), Newport, CA
As the opening quote shows, green building has economic benefits as well as environmental benefits. Here is another statement showing the economic benefits:
LPA estimates that the facility’s sustainable elements will save ENC [The Environmental Nature Center] ~$20,000 per year.–Jetson Green
The predominant system that is used for rating the “greenness” of a development is LEED (Leadership in Energy and Environmental Design). Like all systems, it has its drawbacks and is evolving to address those drawbacks. Here is an overview:
LEED is a rating system developed by the U.S. Green Building Council (USGBC) to ensure that the design, construction, and maintenance requirements result in buildings with some level of sustainability. The current LEED system has four possible levels that a project can attain. These levels, from lowest to highest, are Certified, Silver, Gold, and Platinum. To determine which level a project will receive, points are given for each sustainable feature that fits into one of five categories: sustainable sites, water efficiency, energy and atmosphere, materials and resources, and indoor environmental quality
For example, some of the characteristics that contributed to the Nature Center receiving the highest LEED rating, Platinum, are as follows: The building was designed and constructed in a way that that allows for daily operations that uses less resources than is the current standard. These include the ability to use natural ventilation, less water, and a reduced amount of energy by including solar and wind energy components. In addition, during construction renewable and recycled materials were used, and the building was constructed in a way that reduces light pollution.
For a list of Orange County projects with various LEED ratings, go to the USGBC-Orange County site.