Interesting questions. I suppose I could wear a few hats about it.
a) I am not sure I would blog stuff I want to keep from my partners publicly. It just seems counter intuitive unless you lock down your blog and do invite only. I guess being in the career I am in, if you are online, its public.. period. Privacy is simply a falsehood
b) Is a blog equal to a diary, and heck does that matter. I am not sure, I never believed in the effectiveness of diaries. Again, they were only as private as the people wanting to see it
c) Is it polite to write down information about your partner(s) publicly and not let them review it. This gets sticky. I believe you might have to get permission simply because privacy is so individual. You may appreciate blogging, but your partner may hate it. Thats their right to be left out of the discussion. IMHO. This isn't like counselling where there is an expectation of privacy.. this is the internet. (I have similar opinions on sharing details in a poly relationship. You may have the expectation of disclosure because of your choice, but the people you are disclosing about have a right to control information about them, its only polite)
All that said, I err on the side of caution. I speak about myself now, I didn't always. I also tend to view history. Several years online and poly I see and have seen most of the worst times partially being caused by one partner deciding to communicate with the world the problems of their relationship vs just communicating with their partner. I cringe reading some peoples disclosure and know that I would be annoyed or pissed if I were their partners. And it has happened to me in reverse where I said too much without clearly identifying the boundary.
So, like I said, I just don't. In fact its part of why I went from posting tonnes to posting nothing and now, post a bit. Unless I can relate directly to the problem, I dont try to relay or discuss other peoples stories or emotions. I "try" to avoid speaking for other peoples emotions, situations, problems, feelings. Thats a difficult line to walk..
I work hard to respect my partners right to feel respected. That guides my relationships more than anything.