I read OMB: IPv6 by June 2008 today, which says:
"The federal government will transition to IP Version 6 (IPv6) by June 2008, said Karen Evans, the Office of Management and Budget’s administrator of e-government and information technology.
'Once the network backbones are ready, the applications and other elements will follow,' she said today while testifying before the House Government Reform Committee."
Riiight. Be prepared to see this slip to, oh, maybe never. The Federal government is also supposed to be securing its systems, and its report card is still lousy. Agencies have also known since Homeland Security Presidential Directive 12 (Aug 04) that they needed to implement smart cards, but problems are anticipated in meeting the deadlines.
Marcus Ranum pointed me towards a talk by Bill Cheswick (.ppt) on IPv6 transition realities. It mentions several problems that might prevent IPv6 adoption, like unreasonable demands on routers, hosts which can pick a new IPv6 address for every connection, and other issues.