With any authority, I can only speak from my own usage patterns. I multitask for two reasons - laziness and productivity. Laziness requires a lot of multitasking. It's leaving every tab open so that I don't have to search again later. It's leaving every application open so that I don't have to sit through a splash screen again. Laziness is the epitome of what desktop multitasking can do. Productivity requires far less from the machine, and intentionally offers far less (distraction) to the user. Productivity is keeping data readily accessible in one place when you know you'll need to keep referencing it or copying it to another place. Where laziness is keeping multiple VIM documents open, each in their own window, productivity is keeping the document at hand open, with its corresponding outline open in a split. Laziness is keeping multiple Finder windows open, productivity is having two panes open in ForkLift to quickly move data from one place to the other. Laziness is 100 Chrome tabs, productivity is a press release in Chrome on one side of the screen, a means to write an article on the other (this is what Snap in Windows 7 aims to achieve, and Cinch brings to the Mac).
See a trend there? In my usage, at least, laziness is a cluttered mess, tens or hundreds of windows all existing together because I have 8 cores and oodles of RAM. But nothing about it is clean, and none of it helps me in any way. In fact, there comes a point where it is easier for me to resubmit a search query than to find it in the sea of Chrome tabs and windows. My computer may be faster than my internet, but that doesn't mean I am… Laziness multitasking has no place on the iPad. Productivity doesn't require much multitasking at all. Two is usually enough.
Now here's where I request that you take a break and briefly examine this observation on iPad's aspect ratio by Adam Lisagor, and these thoughts by John Gruber. Particularly pay attention to Gruber's observations on Split Views. What if multitasking on the iPad looked and felt like this? Two applications or instances of the same application, one above the other, much like my beloved VIM splits? I think it's a safe assumption that many iPad apps will be developed alongside iPhone versions. Even if they aren't, they'll likely be coming from iPhone devs. Depending on the app, there already might be a portrait orientation and a landscape orientation coded in - why not a simplified half-view for multitasking? Would it even be necessary, or would scrolling negate the need?
This wouldn't fix everything - the need for a solid notification/state update system for IM, Twitter, etc. would still exist (see Adam Engst's article here). Yet even this is somewhat solved - call it casual productivity. Safari open on top, Twitter beneath. Those distractions should be pushed aside for serious productivity (press release on top, blog editor on bottom) moments. We don't know how multitasking will come to be on iPad, I certainly don't know, and I'm not even trying to speculate. But I think, based on my own usage patterns, a simple system of split panes would suit the iPad paradigm perfectly.