you don't have to give money - you just have to make a promise that you'll do one or more of the things listed. And if you had read the site you would know that.
When I see the word pledge I right away think money so thats why I did not look at the site but now that you sorta said it's more them money I went and looked at the site and I made a pledge that I will replace one light bulb in my house with an energy saving version because that the only one I can do that has not already be done and there lots of trees in the yard at my house.
Excellent! i hadn't thought of the money thing - I forgot that "pledge" could have negative connotations too...oh well, I hope it hasn't put too many people off looking...!