Helps more than you think!
No, Duolingo will not make you fluent. However, it does really help a lot. I recently returned from Huatulco, Mexico. While there I was able to ask for anything I needed, respond to short questions and read all the signs. I am barely half way through the tree. I probably pronounced things poorly and used the wrong words at times but I was understood perfectly! This experience of using the language has energized me for learning more. So, yes Duolingo has helped me learn Spanish!