I'm looking for the same thing. Did you ever find anything?

Try http://www.citeulike.org/user/pigironjoe/article/3833308

And http://elearningtech.blogspot.com/2010/03/twitter-for-learning-55-great-articles.html

Let me know if you find any more

Thanks for the links, Tristram, and I've sent you (by private email - let me know if it hasn't arrived) a document with some of the case studies we wrote up. I can't make this publicly available, I'm afraid.