Next year I plan to get my students to sign up to Twitter at the start of the course (it won't be compulsory though). My hope is that it will help with social presence, knowledge sharing, support and a form of micro-recording as they study. I have tried with IM before to promote this 'I bumped into Jenny outside the refectory the other day and she mentioned this great paper' type of dialogue, but ultimately IM is just a bit to instrusive I feel. So I'm hoping Twitter will be useful - I'll let you know how it goes anyway.
With this in mind, I was pleased to come across Caroline Middlebrook's Big Juice Twitter Guide, which I've pointed my students at (hat tip: Judy O'Connell).