According to my understanding, Android is as multitasking as can be, building on a truly multitasking operating system (Linux) and on Java. Also, if applications don't change their state while they are in the background, you would not notice the difference whether they are open or closed if next time they are opened they look exactly as you left them. If they have to continue working while in the background (like playing music, logging GPS locations, or receiving AIM messages), then put this functionality into services that run in a truely multitasking environment (e.g. I'm sure Android will support multi-core CPUs as well once they are available for mobiles).

The only thing you are really missing is a task-switcher. But this is a simple application that can be built by replacing the functionality of the "HOME" button: Instead of going back to the main screen, it could open a small menu with all "open" applications or the option to go back to the original home screen. The way Android is built, this is really straightforward, since you can easily replace the functionality of pressing that button.

I've put your idea to our list of ideas here: http://code.google.com/p/openintents/wiki/Ideas (under section "First time you use" simple interface)

If nobody else programs this, we should do it, but I'm sure by the end of the contest you will have zillions (or should I say a googol?) of task-switcher applications... (that may organize your tasks according to your preference, show thumbnails of the views, ...)