My concern, as I'm guilty of it as a blogger, is that it changes how you 'talk.'
My blogging voice is light and journalistic - it is difficult to escape this in an assignment, however many references I put on or re-writes I do.
A different mindset is required, literally wearing a different hat and taking a different approach from the start.
As a professional writer I ought to be able to write for different audiences. I'm not sure I can, indeed my voice has always bee the 'spoken word' for TV and Video with scripts design to visualise rather than say anything at all.
I find and consider Twitter to be an invaluable exercise in being succinct; stylistically this has to be a good thing.
However, as I found myself doing recently, something I wrote, after an edit, looked and read like x16 140 character Tweats strung together.
Surely engagement of any kind, a conversation over coffee, over lunch, Tweating or blogs, helps internalise and sought out issues and confusion in the student's mind. It is an activity even if it is being measured?
I wonder if a 'viva voce' in a video conference (Skype, Elluminate) wouldn't demonstrate the value of social networks in education, that it would be apparent that those who are talking about their topic in cyberspace are more likely to have formed some points of view of their own.