What is the Frequent Contacts Book in my Address Book?
Use the Frequent Contacts tab in the Address Book to access your most frequently used or most recently used e-mail addresses. When you send an e-mail message the address is automatically copied to the Frequent Contacts address book. You can view the date and time you last used an address and the number of times you have used it. Once an entry is placed in Frequent Contacts, it remains there until you delete it.