Everyone can, but you decide which ones they see by choosing a display option for each contact.

To choose a display option when adding a contact, click "Options." To change the display option of an existing contact, click "Change" near the image on the person's profile page. If you keep the box under Display Options checked, others will see the person in your contact box. If you uncheck the box, others will not see the person in your list, but you will.