I struggle to find why this is being labeled as the "everything" killer. I'm sure there's a niche-oriented use for the product, but if priced at $599, then from Apple we can expect less for our money so it likely would use an Atom variant that supports the instructions necessary to run Snow Leopard.
And based on that kind of specification, there isn't a single device in my home that it could replace. I could watch Youtube on it, but I'd rather surf the internet with my more comfortable laptop with its LED-backlit screen. (By the way, I recommend LED screens highly, my eyes get much less bloodshot after looking at the screen for extended periods of time.)
I wouldn't be able to play any games without running Windows, and I wouldn't buy any games for it even if Apple offered them in an appstore-type setup.
My cellphone is working perfectly fine with my existing Verizon contract that I'm 110-percent happy with and which won't be up until late next year. It couldn't replace that.
It also couldn't replace my desktop PC which is used for gaming, but also for general purposes like video, audio, and photo editing on my high-res 21.6" monitor which is 1920x1080. No serious computing could be performed on a 10-12 inch screen no matter what.
So, if their new product takes off, I'm not sure what exactly it would kill.