I'd rather see a good email client first, and would rather donate to that :)

For me personally Expose-like thing would only be eyecandy and would be more inefficient way to do the work, but I can see that many people would appreciate it today and have used to that kind of things on other platforms. So, maybe it would be a good thing to attract new people etc, but hardcore Amiga/MorphOS users know how to do their stuff more efficiently by other means :P