Using blogging in the online course could allow an area for students to express their learning through self reflection. 

Microblogging can easily get a quick responce from students. Being that the responces are brief, it does make them think about what they need to write to it can express their full thought.

Allowing students to make up part of the content can be very benificial to all involved. Students can take ownership of their learning and start building a portfolio for their future.

While social netowrking tools may seem like an obvious choice when teaching online, I feel that you need to look atthe desired outcome that you want from the learning, then work backwards to find a tool that will help get your students there. At times, social networking might not be that tool.