How do other characters respond on reading the blog? Are there any consquences to what has been written? My Eileen, if she wrote a blog, would write whatever she wanted and damn the consequences but that is her attitude to life anyway. The Queen would keep a journal which would be under lock and key and several spells to prevent it being read by others as she would not want anyone to know what she really felt about issues or people. (Roherum of course would love to get hold of such a journal and would read extracts from it).
How often would your characters blog? Are there any subjects they can't talk about and why? Would any of your characters be banned from blogging because their public role bars them from keeping any kind of private record? Does anyone defy that?
One good thing character blogging could lead to additional material for websites and so on.