There are a handful of great PR agencies for mobile consumer apps in SF & NY but for a consumer launch, a great PR agency isn't sufficient to garner widespread coverage.

With so much actual product awareness for new apps being driven by Twitter (and to a lesser extent Facebook), traditional PR is insufficient unless the right people are also talking about it the day of launch. Look at Jelly's launch yesterday for a launch done right (at least from a marketing perspective).

With no disrespect meant to PR firms, I really think that spending the kind of dollars they charge for launching most apps is a waste of money. I think with a good directed outreach by you as CEO, you can get enough influencers talking about your product, providing of course, it lives up to the promises.

I think a PR outreach should really be invested in as the app scales, when the kinks have been worked-out, and when there is already a certain amount of buzz. But expecting that the first buzz will be ignited by PR firms is a risky bet.