I am also using the Infopop Ultimate Guestbook. I found a nice German hack that allows you to use an email form on your site. What it does, when someone clicks on the email icon, it takes you to a form where you could contact the person without seing his email address.
Now is there such a hack for UBB?
I already have the ubbfriend email hack that allows recommendations only to be sent from server. The hack that I am looking for is to allow people to send out mail to those members who do not want to display their email address. (On my site, most people do not like to reveal their address, but would not mind getting contacted).