Anyone with "Reporting" or "Administration" user permissions has the ability to opt in or out of the Weekly Digest email:
Head to your Account Settings (the wrench icon in the upper right).
Next, select Account and then My Profile from the sidebar on the left.
And look for this box.
As long as this box is checked, you'll receive that weekly email, so please make sure this is set the way you want!
If you want to turn this checkbox off for another user, preventing them from getting the Weekly Digest, then you will need to edit the permissions on their user name. Ensure that the user does not have the "Reporting" or "Administration" permission, and they won't get the Weekly Digest emails going forward.
(And in case you're wondering, I've included a screenshot of a Weekly Digest email below!)