When the iPad was announced last year, it appeared to be a somewhat risky move on Apple's part, lest it cannibalize Mac sales. Now, just a year later, Apple could take the Mac and shoot it and survive. This has to make the PC maker's blood run cold; Apple is selling a device with 95% of the usefulness of a Windows PC but only 5% of the hassle (to the casual computer user), and they've got nothing to lose if they cannibalize all of their laptop sales.
The breathtaking aspect of this is how just a year ago the Microsoft monopoly still looked unassailable, but now, to some, the iPad's position seems nearly unassailable and on track to capture a huge portion of the casual computer users of the world.