From releases.ubuntu.com:
The Ubuntu 7.04 Beta has been removed to allow space for mirrors to fetch the upcoming Ubuntu 7.04 release. Please check back soon, or download a daily build of the desktop, server, or alternate images.
That says it all. Fire up the torrent client, friends. Get out the spare laptop. Plug your old 733Mhz Windows ME machine into the router. Your bandwidth allocation is about to jump sharply. 😈