I have been waiting for something like this to come up. This may not be the first collaborative online translation project, but it is the first one upon which I have stumbled. AWOL posted the Online Libanius Translation Project, which will attempt to translate the rhetoric of the Fourth Century CE orator into English (much of it for the first time).
I have been expecting this ever since I read the beginning of an MIT-published study on education in the digital age. The study spent a few pages introducing the difference between Information Technology (IT) and participatory media (i.e. user-generated content). One of the findings of the study was the critical difference between the way that modern students respond to the two forms of media: students are more engaged by participatory media than the traditional top-down approach of information technology. Even Perseus is fundamentally information technology because although users can vote on definitions of particular words, there is no real content generated by users. It is fascinating to see a classical project looking for user-generated content.