I tend to only have things open as I need them, but have a number of widgets on the main screen, some of which (Queen Bee) do things in the background for me, which I think should count as a multi-tasking app.

That said, when I do need to multi-task, I usually need to have a few windows open. Being able to open a browser to look up an address, then cut/paste that into maemo mapper to route to the place, then cut/paste the number in to the phone app to call ahead (while in route), and usually add it to my contacts after the call (for later use)...

Not many other phones would let your nav app run in the background, still calling out "turn left on Callance St" while you're entering a phone book entry for the place, or calling them to tell them you're on the way. VERY handy.