In case that last post was a little cryptic, allow me to give an example:
Take, for instance, the guestbook for the new website The Post-. Feed the guestbook into the Guestbook Aggregator!, and you get this.
To the untrained eye, it just looks like some random XML, but feed it into an aggregator, like SharpReader (actually, not SharpReader, because the XML doesn't validate for some reason, but any other one, honest), and you have the last ten, and all subsequent, posts for that guestbook in an e-mail-like format.
Set that up for a few, and you can keep constant track of all your favourite guestbooks.
Eventually, I intend to set up a page that brings together a few guestbooks, but I'm a bit busy to do that at the moment.