Don't bother - it is an amazingly useless service and there are TONS of similar ones. People sign up and then forget about it. It's supposed to be an online address book. Whenever anyone in your friend circle updates/changes an e-mail, phone number, address etc., you get an email notification.
I signed up for it once but I didn't see any rise in spam or anything - so it's clean, I think. (No worries about your email address being sold to spammers....or maybe GMail's spam filter really is that good? I don't know which one.)
However, the one good thing is birthday alerts. So if you have touchy-feely people who hate you for forgetting their birthdays, then yeah, it can come in handy.
Facebook
Twitter