We also use SSN for our college ID (students & staff). We prefer this field b/c it is one of the fields allowed for import and because it only allows a unique entry per constituent, it flags us if we try to enter a constituent who's ID is already in the system. Our IDs stay with students even if they become staff, so it's a wonderful way to confirm that a person is the same and is not a duplicate. Losing this functionality in the move to webview would not be ideal.