As you said, PPC's started of with the expectation that hardware will catch up, which is has. Now it has much less retooling to do than POS. There is actually a number of small programs that take advantage of multi-tasking by displaying stuff in a window. That task manager in my example picture is one of them. There is also sidex, which is a program launcher etc which swoops in from the side of the screen (
http://www.mtux.com/info_sx.aspx ), floating calculators (
http://www.pocketgear.com/software_detail.asp?id=3424 http://www.pocketgear.com/software_detail.asp?id=5150 ) floating sticky notes and even an app that will split the screen. The ability is built-in, and people can and do use it.
Surur