why do you need multi tasking for work?
so that you can run twitter and IM in the background while you're "working" ?
there's going to be nothing to stop you writting a document in iWork, then switching out and reading an email, then back to the document, then flip into the photo viewer, copy a picture, back to document, paste, launch Keynote, put together a few slides, into Safari to look something up on the web
because all the apps will autosave on close, and when you open them, they'll likely go back to where they were last, they don't need to be persistent in the background. and you yourself can only do one thing at once
besides - if you're going to be working, you're going to want to be sat at a desk, so might as well use a desktop or a laptop. the iPad is aimed at those of use who sit uncomfortably on the sofa with a heavy and hot laptop on our legs and just want to surf the web while watching telly