We're not saying anyone should pirate Windows 8, because it's against American legal code and universal moral law, but if you wanted to, it's out there for the downloading. Illegally.
It won't officially hit developers until the 15th of this month, at which point it'll be pirated even more rampantly, but if you want to start now—which you shouldn't because it's illegal!—you could, technically, illegally. Which you ought not to. [The Verge]