If you're reading this, have a quick check now to make sure your profile is up to date with this specific piece of information please: https://www.bookcrossing.com/editprofile/
"Miscellaneous Information" is the 3rd block down.
"Basic Information" asks for Email, Password, First Name, Last Name
"Location Information" asks for Country, State / Province, City, Postal Code
"Miscellaneous Information" asks for Referring Member, LANGUAGE, Date of Birth, Homepage Url (available with Wings membership), Extended Profile(available with Wings membership)
Then it goes on to "Notification Preferences" where you can set your preferences with regards to notifications from the site and other members.
Find this all here: https://www.bookcrossing.com/editprofile/