We just spoke to our SEO for our main stream client work and the guestbook idea is good, but you should try to make the whole hyperlink be relevent to your site. Just getting on the coattail of a GB is not going to help. The prob with doing a keyword rich hyperlink on a non adult GB may mean they remove that entry so think it out if you are going to do this. Not slamming you idea funkmaster, just saying use some additional thought to what you add.
