Lifetime, 86% of money pledged has been to funded projects ($859 million as of this writing). Just 12% has been to unsuccessfully funded projects. (The remaining money is currently live and its outcome undetermined.) The degree to which pledges are truly all or nothing has always surprised us. 80% of projects that raise 20% of their goal are eventually funded. It's a highly efficient system.
That said, I'm glad to head the 20% number :)