UPDATE: the US Postal Service has delayed the May 2011 requirement for Intelligent Mail Barcode usage.
This is from the October 10, 2007 Federal Register:
The Postal Service proposes new address placement requirements for Periodicals, Standard Mail, Bound Printed Matter, Media Mail, and Library Mail flat-size pieces sent at automation, presorted, or carrier route rates. We also propose to require an 11-digit POSTNET barcode or Intelligent Mail barcode on flat-size First-Class Mail, Periodicals, Standard Mail, and Bound Printed Matter sent at automation rates. In addition, we propose related revisions to the address requirements for automation and presorted First-Class Mail flats.
Comments on the proposed change must be received by December 10, 2007. They can be mailed to
Manager, Mailing Standards
U.S. Postal Service
475 L'Enfant Plaza, SW Room 3436
Washington DC 20260-3436