My advice - do your own PR for as long as you can, don't hire a PR firm. I fell prey to the persuasive tactics of one firm, which over charged, over promised, and delivered nothing.
I guess the PR scenario has become more complex with the popularization of social channels, social intent and social influence tools. Also, the fragmentation of communications means the PR manager needs to keep track of more campaigns, people. Indeed, not easy to do if you want to do it well.<p>Just think about the recent PR scandals: AirBnB, the Path contacts-gate, etc. It's very easy to deal with promotion (proactive PR) but very hard to deal with mishaps (reactive measures).
A good PR firm is an enormous help. Having a practiced, impartial judge to help craft your message is valuable. So is someone who already has relationships with folks in the press -- it's the same principle as approaching VCs via entrepreneurs they already know.<p>It's not for everyone, but if spending $10k on building your brand and attracting new users doesn't sound crazy, a good PR firm is a decent place to spend it.