I never stated that multitasking in general is useless. I do that on my Mac daily. I said that it's doubtful that multitasking (such as multiple spreadsheets, watching a movie while surfing....blah blah blah) on the iPad is in high demand.
Here are two scenarios where multitasking is useful on the iPad:
- Communication. People often have to wait for a reply or don't need their entire concentration to communicate with somebody. They want to do other things in parallel. Keeping the conversation window visible in a margin maintains its presence in their mind and stops them from forgetting about it completely.
- Linking to content from other Apps (including the web). People share all kinds of content these days. In many cases, you don't want a total context switch when viewing that content - it has a larger context (e.g. your email inbox, or FaceBook wall, or Twitter stream, or a live iMessage or Skype conversation), and separating those contexts makes for a jarring workflow.
The interesting thing is how desktop OSes solve the latter problem: each content silo is typically within an App or website, in a window or browser tab respectively. However, there is no logical order to them - windows may be freely arranged in 2D space and tabs are an organisational nightmare once you get enough of them.
With iOS, Apple uses a navigation hierarchy paradigm to help you follow where you are (screens slide in and you progress left-to-right, like pages of a book). They could extend that with split-screen multitasking to give you context not just
within Apps, but
between them. That's the way I think Apple are going to approach it - it simplifies all kinds of workflows and makes iOS a really productive OS.