The sin I find particularly applicable to "green buildings" is the Sin of No Proof. Many high-profile projects are advertised as green but no certification can be found to back up the claim. If you are tempted to call your building green without certification by LEED or Green Globes or Energy Star or NAHB or any other third-party certification, do yourself a favor and read the Terrachoice article. Consumers are becoming more savvy when it comes to false or misleading claims and a number of web sites have popped up to search and destroy those claims. Check out the American Public Media "Greenwash Brigade" for example.
A good source for a definition of greenwashing and more links on the topic is SourceWatch.