In your Address Book you have the ability to add 20 pages of detailed notes about your contacts. However, you also have a separate tab in your addresses called the "Contact History." The Contact History allows you and anyone you share your addresses with (they don't have to have edit rights to the address) to add separate entries that give details on when you last contacted someone in your Address Book.
Each entry in the Contact History will list what date the comment was made, who made it, the account name of the person that made it, and what the note is about. You also have the option of adding a follow-up task to your Contact History entry to your To Do List in case there's a future action you need to make regarding that contact.
To learn how to add an entry to your Contact History follow the steps in the image below:
If your "Contact History" notes tab is gray, that means that no notes have been added yet. When notes have been added then the "Contact History" text will turn black. See the image below:
The Contact History can also be powerful when used with the "Attach address to event" feature. When you attach a contact to an event in your calendar, you can then easily add Contact History notes to your addresses from an event. In the image below an address has been attached to an event. You can see how to access the Contact History: