No, it can't, but it really doesn't matter that it can't. Most applications save your place in them, so the only cost of switching is that you have to wait a second for it to relaunch. If you've got a powerful enough processor, then relaunching applications is simply like switching. And because we've got a single-process tablet, there's no slowdown over time, no gucking up as things run dry.

I'd like Apple to figure out a policy that lets Pandora stream in the background, or Last.FM. Those are the only two I care about. Using push notifications for IM works perfectly for me: I see the messages as they happen, which is all I care about.