When you've not posted anything on your blog in a while, but you've been thinking about many topics to write about.
person1: Hey, where have you been? What you been up to? I've been watching your blog, but you're not even writing.
person2: Yeah - I've been mind blogging, but I just haven't had a chance to post anything lately.
The act of composing a blog post entirely in one's mind without ever publishing the post in physical or electronic form.
Bob: Hey joe, what are you doing?
Joe: I'm mindblogging.
Joe: No, I'm just spacing out.