What is Twitterand other micro-blogging tools?
Twitter is a free social networking and micro-blogging service that allows its users to send and read other users' updates (otherwise known as tweets), which are text-based posts of up to 140 characters in length. Updates are displayed on the user's profile page and delivered to other users who have signed up to receive them. The sender can restrict delivery to those in his or her circle of friends (delivery to everyone being the default). Users can receive updates via the Twitter website, instant messaging, SMS, RSS, email or through an application such as Twitterrific or Facebook. (Wikipedia)

Get a Twitter widget

Twitter & Education - #140conf LA from RealPlayer SP on Vimeo.

Twitter Lists in a Nutshell (YouTube)

Background and guides

Twitter in Plain English

Clay Shirky on How Twitter Can Change History

CNN's Howard Kurtz on why journalists are tweeting

Twitter Hashtags Explained

Building your network:

Searching Twitter:

More on microblogging and backchanneling:
Just for fun