if it makes you feel any better, i find that having an offsite guestbook(like an atabook) doesn't really effect how i think about my site. i think it's a good idea to have a guestbook so if theres a glitch someone can let you know. of course, its your decision, but i think it's a good idea. i'd definitely sign it ;)
for me what Just Works is setting the body's width with max-width so the browser does the magic itself XD then again that only allows for a single column layout unless you get clever with it