[dirkdeman]

As a former PR professional, I can tell you that publicity can be bought. Good publicity however, can't. A post on TechCrunch/Mashable/Wired/whatever is infinitely more valuable than a facebook ad alone. Having said that, you should develop a strategy that involves both paid and free publicity. If you set up a guerilla marketing campaign, an advertising campaign and a free publicity campaign they will fortify each other. Someone sees your facebook ad, and a litte while later reads an article about your startup on TechCrunch. A few days later he sees your brilliant guerrilla marketing thing, hears from other people that they've signed up and signs up himself.

There is no single way of getting publicity, no silver bullet. It's a snowball effect, several small pebbles thrown in the right spot at the right time will cause an avalanche.

And yes, you should post on HN first.