Can to do lists make you unproductive?

I just read the article by Derek Sivers about not speaking in the future tense ( http://news.ycombinator.com/item?id=961654 ). In it, he references another of his articles that argues announcing your plans decreases the likelihood of achieving them ( http://sivers.org/zipit ). It has been said that writing a letter to a dead relative can be a cathartic experience despite the intended recipients of the letter never reading the contents. So in the same vein can writing to do lists simulate communicating our intentions and consequently widen the intention behaviour gap?