I think that it's great idea to generate more information automatically; but, to be honest, I haven't used git notes yet. For important or bigger commits I usually use the extended (longer) commit messages. I think that there are a few things that should be considered:
1) Where this information should be displayed - together with the commits or separately? I would vote for showing them together. If it was separated then it would require additional effort for rephrasing to make the text clear, fluent and meaningful - this would have to be done by the blog maintainer (by Aslak or by you) because I don't know about anyone who have succeeded in running the project (arquillian.github.com) locally (except for Aslak).
2) Usually one functionality that should be mentioned in the blog post consists of more than one commit. So, I guess that the note should be attached to the last commit that implements the functionality, right? Or it should be described incrementally?
3) Isn't better to retrieve and parse the extended commit messages?
I've got these concerns because I don't have any experience with git notes and I cannot imagine the process of retrieving and formatting the texts... I'm not against it I don't have problem with learning and trying new things I'm just afraid that the effort will be bigger than the results (not only for the commiters but also for the blog mainainer)...