The first million people to sign up can get their first taste of 10.10 today.



From ArsTechnica:

If you didn't sign up for the OS X Yosemite public beta after reading our preview yesterday, you should do it sooner rather than later. Apple has just released the software to its Beta Program site, and people who have signed up should be receiving their notification e-mails now if they haven't gotten them already. Beta testers will receive a Mac App Store redemption code for the software, at which point they can download it as they would a standard OS X installer.

What to do if you want to try the software without relying on a beta every day.
Since this build of Yosemite is beta software, you should back up all of your data and treat the release as though it could wipe out your entire hard drive at any time. Time Machine is your friend. Use a Mac you don't rely on day-to-day if you have one, or at least make a separate test partition after backing all of your stuff up.

  Download the OS X Yosemite public beta now