Guestbook backlinks useful?

Are leaving backlinks via a sites guestbook useful backlinks?

And does anyone know if they are do-follow, or no-follow links?

I've always been a manual blog commenter person, but guestbook comments are easier, so I'm just wondering.

Thanks.

It is similar to blog commenting. If it is high PR, do-follow & anchor text allowed, then its good for backlinks.

And does anyone know if they are do-follow, or no-follow links?

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Mostly they are set to no-follow to avoid spamming, but still you can find many do-follow guestbook pages.

It's hard to find a guest book which hasn't been spammed to death so unless you find one of those I wouldn't say there too useful.