Marc Milgrom, thank you for your post. I was not aware that you could go through the assessment without applying for the certification (for which, as a non-incorporated sole proprietor, I don't qualify). I started the process and got a logon, but I'll wait until February to do it because they announced they're putting up a new version after this month. I expect it will be a nice tool to offer in tandem with the simpler assessments I designed to help my clients self-evaluate (which are available for use at no charge at http://impactwithprofit.com).
I do believe certifications and other 3rd-party validations make a difference. I've had a number of people comment that things like my Green America Gold Certification (I was the first business ever to get this, and had to train them how to work with a sole proprietor who has no employees), my induction into the National Environmental Hall of Fame, and the endorsements of my books by green biz experts like Joel Makower of GreenBiz and Jacquelyn Ottman, author of The New Rules of Green Marketing--as well as endorsements by marketing luminaries including Jack Canfield of the Chicken Soup Books and Seth Godin with his dozens of marketing best-sellers--influenced them to do business with me.