Steve Ballmer announced during his CES keynote the immediate availability of the Windows 7 beta to TechNet Plus and MSDN subscribers.
The keynote also included demos of how Windows 7 is faster, more reliable, and makes it easier to do what you want.
Steve also mentioned then that an open download of the Windows 7 beta would become available (already is now).

Additional facts gathered from blog posts:

  • The public beta will be limited to 2.5m downloads
  • The beta will expire on August 1st, 2009
  • A public beta of Windows Server 2008 R2 is also available

Relevant links: 

Interesting comments: