Even though I've had a twitter account for a few years, it's only been in the past few months that I've made extensive use of twitter. (if you want to check out that usage, I'm @larryfeltonj there as well)
Recently an account and hashtag was set up nominally to protect progressives against "spam blocking", and in response to #TGDN, the lunatic right's equivalent project.
I'm skeptical about spam blocking as a primary reason for spending a lot of energy on lists and hashtags. But #UniteBlue has turned into a very interesting and useful means of connecting progressives on twitter. Other lists and hashtags have tried to do the same, but #UniteBlue seems to have gotten further, and yesterday helped to get the hashtag #SaveUSPS trending. In and of themselves hashtags are an echo chamber, but as a platform to convince people to take real world action they could be an excellent platform. At minimum members on #SaveUSPS were being encouraged to go to their rep's website and send an email.
I've written much more extensively on twitter usage in this tumblr blog post.
If you are a twitter user and haven't checked out and thought about @UniteBlue / #UniteBlue yet, you should do so.