The Hollaback iPhone app does pretty much what you'd expect it to do. If you're being harassed or are witnessing someone being harassed, you can whip out your iPhone running Hollaback, take a photo of the violator and upload it to the Hollaback servers along with location data. A follow-up email comes back to you later, where you're asked to detail what happened. Once that's done, the scumbag's photo and your story are posted for all to see on the company's website. Though the US$0.99 app is now available in the App Store, I wasn't able to test it out because, well, I doubt I'd find volunteers to try it out on.
Allowing these incidents to be reported so quickly and easily could be a great way to help authorities nail down problem-ridden locations, but I have to wonder if whipping out a cell phone rather than running away or calling for help is the answer. Maybe you're better off pretending to make a call. Also, why is there a price tag on this app, when it was reportedly paid for already with donations?