Some time ago we used an other guestbook which we had to close down after just some months. Cleaning out hundreds of spam messages was complicated and very time consuming.
We changed then, on Joomla! 1.5, over to Easybook Reloaded, on one of the first versions. Spam significantly has been reduced, although not to zero, but to one or two a day. We did all the updates and started to use ECC+ as well, which drove us down to almost zero!
As Easybook Reloaded gives the possibility to delete an entry by just klicking on the provided link in the e-mail message, we were happy to have this extension!
Now, some weeks ago, we changed over to Joomla! 2.5 and installed the latest EBR build. Although we are using the same domain we did not receive one spam mail!
We are very happy with this solution and are sure, that it really serves the Joomla! community. As a sign of gratitude we bought a membership with Kubik-Rubik.