I don't think creating buzz prior to launch is that necessary for most startups. The question is more how to get a lot of people to the site after there's something to do there.
If you wish to make a pre-launch buzz, try it in a controlled environment. A strategy I used was to aim for foreign startup blogs (mandarin, spanish, french, etc) instead of western ones. Their reviews gave me a leg up on the feedback I should anticipate from western bloggers.
Since the initial buzz I generated centered around foreign bloggers, I did not risk losing my reputation in front of the big name Web 2.0 startup bloggers. I took my startup to the west only after I was satisified with the feedback.