Just noticed another key difference between the two (blogs and forums) tonight. Call me slow, but I noticed that when posting a blog, all comments are intended to be for that blog post. Whereas, in the forums, you can post a general comment on the forum topic or post a response or comment specifically to someone else’s comment.
For example, Scott Horvath posted a Blog, actually a question on the use of Twitter by a government agency today. He should have posted it as a Forum as there are some intereseting comments that warrant a response not jus to the Scott’s post. Unfortunately, you can only post a comment and not attach it to someone else’s.