Geeks of the world went through a collective wave of anticipation and lament yesterday at the unveling of the Apple iPad. If there was a single most missed feature, it was probably the lack of multitasking. I'm going to say something contrarian here. The iPad doesn't need multitasking now, and possibly not ever.
With the iPad, Apple is taking a step down the path where separation between interface and application (or Model from the View and Controller if you prefer) is not just a convenient software architecture boundary, but is an actual physical interface boundary. As much as you might wish it, humans are, at best, serial-taskers when it comes to interfacing to a computer system. Notice I said system. The next logical step after the iPad is to seamlessly connect it to other higher horsepower devices; devices on the net, or devices in a cloud. Personally, the link net devices are fairly mature over the browser, but I'd like to start maturing the link to my personal, home computing devices, the cloud can come later.
If the iPad is just an interface device with just enough computing power to ease local controls processing, you can then multitask to your hearts desire by giving server type devices tasks to go off and perform. Basically, as long as you can push images onto the iPad and control commands back to a server, and do lightweight processing for compromises between those two extremes, you can think of the iPad as a physical manifestation of a application gui window on your desktop computer.
The only thing you need is a multi-event notification system, which iPhone already has a least laid a foundation.
There are some short-term, established ways to pursue this link, the X window system is a prime example. For more recent examples, you could look at VNC/Remote Desktops type applications to extend your interface device. Ironically, the VNC/Remote desktop applications are less rich than the X system. And of course, browsers are increasingly delivering reasonably responsive application over web technologies. This should only get easier with the rise of HTML5. However, Apple has always dabbled in interesting interface and display technologies. I'm hoping that Apple has it's sights set on a longer term view of this path and is preparing some newly rethought method of linking server side power to an exportable iPad interface that may blow the doors off of all these paradigms.
