I personally love the idea of using Twitter as a prompt for blogging. One form of digital writing compliments another. Send students to Twitter to find what people are saying on a given topic and then take some of those quotes back to the blog for responses. They could, of course, simply reply on Twitter, but taking the Tweets to a blog for response allows for more involved reactions and, we hope, more depth of thinking.
Students don’t have to blog to use Twitter for writing prompts, though, not even of the deep thinking variety. They could write their responses in a journal, or they could type them in a word processing document. The act of mining Twitter for ideas and thinking through those ideas in writing will be the same either way.
They might also look for creative writing prompts on Twitter. Photos make great writing prompts, for example, and Twitter is filled with photo-bloggers linking to their sites. One of my current favorites is @unhappyhipsters.
I also love the Twitter-related sites that pull in Tweets for comic purposes, such as the site Tweeting Too Hard. A good creative writing exercise might be to write a scene with a character who might have written one of those tweets (without actually stealing the tweet, of course). Another of these sites that leans toward hilarious is favstar.fm. Not all of the tweets are PG, however. Depending on where you work and how old your students are you may have to select some tweets for them to use as prompts. I believe in standing up for creativity wherever possible, but there is such a thing as asking for trouble.
Use your imagination. Ask your students to apply theirs. The possibilities for finding writing prompts on Twitter are virtually endless.