Replacement by laptops is what I expect to happen. The power savings of a new Sandy/Ivy Bridge laptop will pay for it.
I am buying non-touch Sandy Bridge laptops for sub-$300 and distributing them to my kids as 2nd and 3rd PC for their children to use. Touch versions are $500. These laptops do not need any expansion. They need to access the WiFi printer and not much else. The mouse is even bluetooth so no cable.
Unless you need to add some extra equipment (graphics, Intel PHI, ....) to your system, a laptop is fine.