Apple's next-gen OS, Mac OS X 10.5, aka Leopard, is expected to ship in Spring '07. This is not a secret. But somehow we feel better when Amazon confirms it for us. As Nelson pointed out in the iWork '07 on Amazon comments, they are already listing Leopard with a note that says "Scheduled to ship in spring 2007."
Amazon is conveniently offering to email you when it's available for purchase. I guess Mac lovers who plan to be in hibernation for the next 3 months might need that.
Thanks Sean and Nelson!