Good work.
I'm intrigued by the idea of Twitter stream as formative/summative assessment. It would be interesting to see how to build this model up in your classroom. You'd have to identify ways to do so while protecting students, respecting "terms of service" from the companies, and respecting the AUP of your final school/district. Despite those constraints...I think it would be a powerful form of learning, and perhaps a better (more ecologically valid) form of assessment.
Looking forward to seeing you test it out in your classroom. Keep blogging. :)
Badge awarded.
-Ian