My two Brazilian friends, Erika and Carla, in their Blog It! blog, produced the following list of advantages of blogging in an EFL environment:

Why blogging?

• Writing for a real audience
• Extra practice of reading and writing
• Creation of somebody’s or a group’s own multimedia environment
• Students’ work can be read by their peers
• It builds up a sense of community
• The practice of English goes beyond the classroom
• The online environment encourages shy students to express themselves
• Students can get replies from all over the world
• Relatives and friends can see what is being done in the classroom
• No technical expertise needed
• It enhances creativity
• It is a rich learning space

I'll try to build upon it as my knowledge grows.

See this link for a list of pros and cons of blogging in the classroom.