It would seem that following the ‘deactivate account’ link in Facebook does not actually delete your account or remove your profile. Your account just goes into a limbo state and is automatically reactivated if you log in again.
If you want to permanently delete your Facebook account, follow this link to http://www.facebook.com/help/contact.php?show_form=delete_account
After submitting the form you should receive a confirmation email like this:
Subject: Account Scheduled for Deletion
We have received a request to permanently delete your account. Your account has been deactivated from the site and will be permanently deleted within 14 days.
If you did not request to permanently delete your account, follow this link to cancel this request:
The Facebook Team
As long as you do not log into your Facebook account again with two weeks then your account will be permanently deleted.
Update: Have a read of Gizmodo’s Top Ten Reasons You Should Quit Facebook if you weren’t convinced already.
See http://www.groovypost.com/howto/security/permanently-delete-your-facebook-profile-account/ for more in-depth instructions on how to permanently delete your Facebook profile.