I agree with many of the perspectives and projections in this post but I have a different opinion about the likely implications for traditional PCs.
When Apple first announced the launch of its iPhone platform, we wrote here that it is a game changer. Even the core of iPhone is a major advance in mobile computing, but with the platform iPhone becomes the new personal computer. The desktop from now on will be for professional and business work. Laptops aren't going away, but will get increasingly less personal use. The reason is that iPhone with its application platform is a better personal computer and it's widely accessible.
My $.02: I think iPhone-class devices will make PCs more rather than less useful, as the devices will facilitate doing more with digital information and communications, making it more useful to have PCs that will, in combination with myriad Internet services, essentially become personal servers.