Psychology tests show that announcing your goals makes you less motivated to accomplish them.
For the TED Conference, you can submit a few different ideas for a talk you'd like to do. For this TED, I submitted three ideas. Two I was excited about, and one as an afterthought. Of course they chose the afterthought: this talk.
I'm really no expert in this subject. I had just read an interesting article in Newsweek Magazine about this, then did a little sleuthing to find the original research, then presented what I'd found. Total time spent: maybe 5 hours. See the original article, full of links to more information, at http://sivers.org/zipit
Since people on the TED stage are usually experts, people have taken this talk far too seriously. It was really meant as just a 2-minute eyebrow-raiser. A little something to think about. That's all. But over 400 comments arguing about it on the TED page for it: http://www.ted.com/talks/derek_sivers_keep_your_goals_to_yourself.html
But I wish I would have included one important point, that makes a lot of difference:
These studies are only about IDENTITY GOALS : goals usually related to personal development, that would make you a slightly different person if completed.
This does NOT apply to things like starting a company, brainstorming, or other pursuits where it would be useful to corral a bunch of people to support your project.