I think the Zaurus doesn't and generally wouldn't do well in the US because the stock software (like the PIMs) just don't work real well. Plus, so many people are using cell phones for a PIM device, that they usually don't even need a Palm-type PDA.
I like the idea of Sharp making the hardware and then having someone else brand it and I think someone else should be making the software to run on it. I work with a lot of people, who like myself, are big Apple people. When they saw my C760, they said "Wow! It looks like a tiny iBook." I'd love to see Apple partner with Sharp the way the did with the PortaPlayer people for the iPod and come out with a mini-iBook like PDA. Perhaps they could spruce up the look of the Zaurus to be more like the iBook (a glowing Apple on the top and pulsating latch light would be cool), port Darwin + Aqua-lite interface + iCal/AddressBook + iTunes + Quicktime.
Alas, I think it's all a pipe-dream, but it would be cool.