Freakonomics rejects that notion, but I felt that they were talking about different things.
Publicly announcing a goal like running a marathon, or losing weight, is a respectable and well-trodden path. Despite some tag-along negativity, the overwhelming theme is supportive; one draws energy and motivation from the crowd of supporters.
For things that are revolutionary, unorthodox, or downright unreasonable, talking about it may not be the best solution.
I'd wager that Albert Einstein achieved most of his best work in discreet isolation. It's probably the same way Apple loves to keep its plans secret.
This sort of virtuous secrecy is something that boosts creativity and productivity manyfold, and should be upheld.
In these sorts of situations, I think its wiser to err on the safe side, and keep your evil plans to yourself.