event handing - skype calls arriving, new mail, facebook updates. This is what push notification is for.
task switching - go from yelp to map to safari to monopoly to back to yelp. This sounds like what the expose interface would be for. Apps get suspend events and then are just frozen until they are switched back. Then they get a resume event. They don't run in the background at all, they just pick up where they left off.
background tasks - the only area where true multitasking is important. Pandora playing music, GPS tracking, downloading. I think Apple will only allow this for specific services through a background management API. They'll start with a very few use cases where an app can register to play music, or maintain a network connection, or similar and add more services as people come up with new things that really require background operation.
The article talks about multitasking but there isn't really enough information to tell if it is more than just task switching, which is what I think it is. That would still provide a huge percentage of the benefits people actually want from multitasking, and with zero battery impact.
I don't really get how task-switching improves things from where they are now. The iPhone OS - or rather iPhone apps - are supposed to save their states so that when you return to them, you're right back to where you left off. All the apps that I use do this perfectly, even games.
I remember when the Palm Pre first came out, and people said "I can leave my browser, flick it away and send off an email, and then flick back to the browser and I'm right where I left off. You iphone users try that!"
But iPhones do exactly that right now without "multitasking." If you click the home button, go do something else, in most cases when you come back you're wherever you left off.
Adding some additional expose-like UI for task switching would seem to me to just clutter things up while adding nothing.