Instead of teaching how to use a hashtag and how to tweet and retweet, I give my students meaningful tasks to help their learning. (Twitter plays a large role in my teaching, but the essential elements can be applied in many technological contexts.)
I like the idea Bali has with this. Prof. Station has been doing similar things by asking us to engage in discussion over twitter, using the hashtag #FYS156. I think it is a very effective way to communicate and express ideas to a wide variety of people. It is also easy to see other people's thoughts and opinions to perhaps gain insight on today's issues.