How I Use It
I've used Edmodo numerous times--it requires some setup in that the teacher has to organize everything ahead of time but once you've put some time into it you can see that it is a smooth interface that seems to ape Facebook quite a bit. The similarities between Edmodo and Facebook's look are so close that most students can intuitively navigate the site without too much bother. Once there, you can create small groups that only certain students are a part of and use that to launch an actual assignment. It's nice because everything is paperless, including the grading.
The students can customize the platform quite a bit and may enjoy adding their interests, pictures, etc. Interaction with one another can be moderated to your heart's content, ranging from zero interaction to full discussion threads. It's a nice and controlled website that has endless potential.
The students found it easy to use but thought it was a bit dorky so there was some aversion to playing with it beyond the initial rush of excitement that comes from something new. I found some of the grading that I did through the program to be a little awkward to use since I'm not using 100% Edmodo to track student grades. Make no mistake--this site wants to be your be all, end all and probably works best when you use it for *all* of your assignments and interactions. If you are only using it for one quiz here and there, it will tell the student that their grade in the class is the same grade they received on the quiz. Potentially confusing.
I prefer to use it to organize students into groups and give them a "home base" to ask me questions and interact with one another.