How I Use It
I use Edmodo to manage an 8th grade Algebra class. I post announcements, practice problems (in the form of quizzes), and notes using Google Docs. It has worked fairly well, with the exception of the quiz limitations that I mentioned earlier. I also teach some high school classes, and I tried Edmodo with one of them, and the students complained that the interface was too simple. They actually prefer Schoology. That tended to be the general sentiment among students in high school, so we made the decision to use Edmodo in middle school and use Schoology in the high school (we are a PK-12 school).
Edmodo is a great social learning platform (Edmodo's CEO claims that they are not an LMS). It is great for communicating with students and parents, organizing course content, posting announcements and assignments, and giving some basic assessments.
One thing that could definitely be improved is the quiz feature. When creating quizzes, Edmodo offers multiple choice, true/false, matching, short answer, and fill in the blank. There are no real formatting options when creating questions, and you can't add pictures and links, which is a real limitation for some of the questions I would like my students to answer in math. The quizzes are also limited to a 24 hour time limit. I often create quizzes just to be used as practice on certain topics. If a student starts on a Friday, they must finish 24 hours later (on Saturday). Currently, there is no way around that.
What I do like is that they have made some significant improvements over the last few updates. You can now filter posts by type (quiz, alert, assignment, poll, etc), instead of all posts appearing in one long stream (like Facebook). I also like the ability to create small groups within your classes, so that you can better manage students or group students for differentiation purposes.