Our impressions of Duolingo is that they do a very good job of covering around a semester of college language study and making it fun. That's a handy thing to have in your head when you're starting out.
In terms of eventually moving towards fluency and away from translation, We don't feel like Duolingo can really do that, since their product is translation, and so they can't really separate their users from translating. As a collective, we find that while it's feasible to learn some useful content from Duolingo, it's faster and more efficient just to skip that and jump straight into SRS use without translations.