Friend David has done it again, succinctly given us the short course on communication. Check out his notes about communicating in the 21st century here, at his 2cents Worth blog.
Want some justification for why we should be emphasizing communication (not just 'writing") in our classrooms? Read this article at the Partnership for 21st Century Skills website. It's about the critical lack of same in the sadly lacking emergent American workforce.
Finally, I'd submit that blogging is one Web 2.0 technology that can enhance our students' communication skills in inumerable ways. See supportblogging.com for much more on the topic.