There's a lot of mythology around writing, but the truth is simple - you learn to write by doing it. The more you write, the better you get. And I'm not specifically talking about blogging here, but all forms of writing. A few smart people figured this out hundreds of years ago, and it became the Oxbridge tutorial system - students write on a regular (e.g. weekly) basis and their work is critiqued by a tutor in a one-to-one setting. There's no place to hide, and at the beginning it can be brutal. And it works. It's how I learned to write as an undergraduate at my thoroughly redbrick university, taught my by Oxbridge-educated tutor.
So if we know that it works, why don't we use it? "Resources" - which you can interpret either as too many students or too little will to implement it. At present, most of our formal taught postgraduate sessions are squeezed into one or two hour slots. Which is fine, if you're trying to teach people how to click buttons, but it's not going to have any significant impact on writing skills. There's no alternative but to bite the bullet and do it for real.
So how could it work? The Graduate Studies Board also discussed the possibility of assigning credit to these taught sessions and requiring all postgraduates to gain a minimum number of credits from a mixture of compulsory and elective sessions. Students would be asked to complete a set program (for example 6 pieces of writing over a over 12 week period?) to earn the relevant number of credits for the time spent. It could be run in blog format, but for this group my preference would be to replicate the same format that they will be writing in for publication, either using Microsloth Word or possibly shared Google docs. Supervisor buy-in is a key aspect of these taught programmes, so maybe supervisors could be asked to look at the first and last submissions so they could see how the students have progressed?
The obstacle is still staff time - so if there's no will to implement a full scale programme across the entire College, I'm inclined to try to run a Departmental pilot via the Roberts fund. Are you in?