Here's a nifty study on its effectiveness to teach Spanish to English speakers.
The study estimated that a person with no knowledge of Spanish would need between 26
and 49 hours (or 34 hours on average) to cover the material for the first college semester
of Spanish. This result is based on the language test's cut off point for the second college
semester and the 95% Confidence Interval of the effectiveness measure.
If you speak English, there are several courses you can take, such as French, Brazilian Portuguese, Dutch, and Irish. They also offer courses for people who speak other languages.
Personally, I feel I've learned more German and Danish in a couple of months with Duolingo than I have from 6 years of French in elementary to high school. It's fun, too. Were it not for Duolingo, I probably would be stuck with English and three Canadian French words because I've never really found enough motivation to keep learning a language until now. It helps that you somtimes get to translate gems like "jeg ved din hest drikker vin" (I know your horse drinks wine). You gain experience from completing lessons and level up accordingly. And you can compete with friends, seeing their progress on the leaderboard.
Interested? Let's be Duobuddies and shove each other off the leaderboard! I go by the username Tumthe3.
Our Duolingo members