I agree with you, missingno15. I suppose it really only makes sense in objective texts, such as found on Wikipedia. But generally I really like the idea that this way big parts of the web could be translated in different languages. People, who previously didn’t have access to that information suddenly could read and understand it. Also given a sufficient number of people taking part in the project (i.e. millions) the translation will be done much faster than if performed by paid individuals.
Regarding the missing context, that is a worry of me too. The meaning of a single sentence can vary drastically depending on its context, and that is of course not only in Japanese, but really in any language. I’m looking forward to see how they want to approach this problem.
Finally, I think this could be a fun way of learning a new language. But only as long as they don’t exploit the users. It would kind of have an akward feeling to it, if you knew that they were earning tons of money with your work, even though technically you learned something and have no fees as in normal language learning programs.