I simply dont buy the fact that PCs are all going to become appliances in the future. I dont doubt that some form of this will arise, and it may be good enough for the masses, but buildable, customizable PCs arent going anywhere. In fact, I think it will ALWAYS be cheaper to build it yourself.
For example, look at audio. Back in the day, if you wanted to listen to music, you had to buy a amplifier, two speakers, and a turntable. Sure, you could buy them together, but mini-systems as we know it didnt exist. They came about eventually, but did that spell the death of the component system? Absolutely not. Most people do elect to go with a mini-system, but if you want high quality components, putting it together from separate pieces is the only way to go. You can now buy HT in a box, but they suck compared to full components HT setups.
PCs in their current form will always exist, because people like me are going to pay for them. I'm not buying no appliance PC in the way I'm not buying no silly mini system. I might buy them for other people, but not for me. If theres a market for it, they'll make it.