Why not expand on the concept that people could use a place to store an annotation of any sort. That way, if I want to leave people text, photos, a presentation, an embedded video, etc, I can do that without the need to create a blog or let that person see a full history of other things I've written. Another idea would be to generate a QR code for the page.

That being said, I can't think of very many times I've needed something like this. If I had more to say on a topic than I wanted to leave in a comment, I'd blog about it. If I knew the person, I'd email them.