Re: Guestbook getting spammed!
Yes CAPTCHA is a good solution but not good in all cases. Most prolly you have your guesbook hosted on a shared hosting. In that case you might not be able to implement CAPTCHA for certain reasons.
Usually this spamming is done through automated bots. Mostly these bots are configured for a certain template and run all over internet lookking for websites they can recognize. So what you can do is change the flow of your guest book application a little bit. For example you can add a checkbox with yes/no option asking user if s/he's sure about adding this comment. Having this added, automated intelligent (actually stupid) bots will not know that they have to click 'yes' before adding a comment unless someone will program them to do so.