This would be better than having an external guestbook because:
1. Use just one interface to handle the guestbook, rather than two.
2. Protect your guestbook from spam if you have WP secured.
3. The guestbook fuses perfectly into your website theme.
I’m sure there are more reasons, but I can’t think of them right now.
She already provides you with a guestbook template for quite a few common themes.
And I am planning on releasing a Guestbook Template with my latest release of Connections Reloaded.
Don’t know if I would ever put a Guestbook on my blog, but I’m seriously considering using the WordPress Paged Comments Plugin, since many page already have a lot of comments.