Personally, I'm a bit skeptical that enough folks will participate to cause a blip on the Treasury's radar. However, I'm curious to hear what others in our group think of this.
Even the organizers of that event recognized that the small amount of money involved in such a protest isn't going to be noticed by anybody. Their optimistic figure (if 1,000,000 people cash in bonds averaging $100 each) is $100,000,000.
The part of the protest that might be a little more effective is if 1,000,000 people send in the letter suggested on that site, or one like it, to their elected representatives. Those representatives would see that one million people cared about the out-of-control spending enough to take some action, even if that action was fiscally insignificant.