I really like Edmodo. The user-friendly interface is something that will appeal to a lot of educators and I like the idea that students do not need an email address to to join your group.
The idea is that you, as a teacher create an account. Once you have done that you can create groups that you manage. I have created a group called SGD 2012. Edmodo then creates a unique code for you group. You pass this code onto your students they enter it into the website, they fill in their name and some other really basic details and voila! You have a secure way to communicate to your class online. Using Edmodo you can send messages to students assign homework, learning tasks etc. This is a great way of ensuring that the learning can continue whether at home or school. If you put classroom tasks onto Edmodo and use you interactive whiteboard to display the material you ensure that you can revisit previous material easily and any students that are away can log in and catch up on anything they might have missed.
Have you used or do you intend to use Edmodo in your classroom?