When they first started using it, it was great. We got little notes here and there and left comments for them to read the next time they found a cafe. Then the comments started disappearing. I thought it was odd, so I dug into it a little bit deeper. It turns out that they delete the comments after they read them so that they don't waste valuable cafe time looking for comments sorting out the comments that they read and the ones they hadn't. After reading, they delete and therefore any comments that are left on their blog are unread (by them).
Which almost completely defeats the point of the blog. This was supposed to be an effective way for them to keep in touch with us and vice versa. It was also supposed to be a scrapbook that they could enjoy when they got home. Unfortunately, a defect in the design of the application will likely prevent this. As it is, the archive is incomplete - and stopping them from deleting the comments as they read them is likely not going to happen. After all, time is money - especially when you're on a tight travel budget halfway around the world and the meter on your blogging session is ticking.
Happily, the solution is simple. Blog application developers need to figure out a way to allow readers to mark items as read. I'm pretty sure that this is something that has to live within the content management system at the application layer - or better yet, the browser itself. It could be automated or manual as long as it is simple. In fact, it must be at least as simple as the MT "delete comment" function.
Now go build something. ;)