Update: GigaOM reported that the rollout was premature. Those outside of the US and Brazil who successfully signed up for the program will have their money refunded, and Apple has told these customers that Match will not function outside of those countries.
iTunes Match has started rolling out in markets outside the US. International users have said that signups are now available in the UK, parts of Europe, and Australia. Here in New Zealand, I can confirm directly that iTunes Match is available as a signup option in my NZ-based account, for a fee of NZ$39.99 per year (compared to the US$24.99 per year it costs in the US store).
Signup links aren't showing up in the main pages of the iTunes Store for international users; instead, you have to navigate to your "Account" page to see an option for the signup. Some sites, such as Mac Rumors, have suggested this means iTunes Match has been accidentally revealed early to international users and therefore may not function as expected.
UK users will pay £21.99 for the service, while Europeans will pay €24.99. Australian users pay similarly higher fees at AU$34.99 per year.
iTunes Match allows users to mirror their entire iTunes libraries in the cloud, enabling near-instantaneous playback/download of any song in the user's library on any connected device.