I've been thinking, the problem with the Pledge from Live Earth is that it's done in a transient way. Text to the number given, count the pledges sent in per city, and declare a movement. But Oprah understands that pledging in that way lasts only as long as the high of the moment does.
Fall Out Boy wondered about that, saying save the environment is like working out -- you only do it when it's convenient -- and wondering if this intention will burn out by the next concert next year (there's going to be another one???). That's why Oprah tells her viewers to print out a contract, personalize it, sign it, date it, and post it prominently. That's how to keep one's intention live, that's how to turn a pledge into action.