I've been thinking about this recently, since Aleks Krotoski's talk at The Digital Researcher 2011 in which she touched on the social media echo chamber, and closer to home, in watching dissent spread as students get themselves worked up on social networks.
So far, my reluctant social media policy has been to enforce use of social tools though assessment. I have done this with a range of social tools over the last few years. Done well, you can expect 10% long term take up rate (some months post-assessment), as opposed to essentially zero without any compulsion to engage.
But should I continue to push this approach? Would it be better instead to offer my time to a minority coalition of the willing? I've never managed to build a convincing extra credit model within our assessment schemes, but delayed gratification remains a tough sell in education.
These decisions are crucial in the ongoing struggle against over-assessment, but I remain uncertain of the best course to follow.