Skribit is a great idea. I think it's still very young and has a lot of room to grow, but it's a terrific start and the first of its kind.
I've run into this problem quite often when trying to keep up with my readers. Thanks for the feedback though - how can we make it more apparent that we are solving the "writer's block" problem?
If I have a blog for subject, I would still like to understand what it is my audience want to know more about such a subject as to guide what I write in the future.
What this is supplementing really is just email, in a more passive way.
Most bloggers i know, write because they are genuinely interested in an activity/thought/event. If someone writes about something they are not really interested in (or knowledgeable about), it would be plainly visible. (One of the exceptions i can think of are people who write pure fiction like short stories on their blog ala writers.)