Here are a few Twitter links that you might find handy. My Diigo list is much more comprehensive but it is really disorganized.
Why Use Twitter in Teaching and Learning
Twitter - A Teaching and Learning Tool
A blog post about using Twitter in the Classroom by Tom Barrett.
A collaborative ebook written by teachers for teachers about using Twitter effectively.
@kchichester's Twitter Diigo List - I post all the links I find helpful about Twitter to this Diigo list.