A complete, adaptable OS would be nice, so you could just add functions like this later or someone third party could program them for users.
I wouldn't mind an option to cache the google maps for your local area (eg. city) either. So you could navigate better offline. (not sure how large they would be). I think it already caches where you've looked last, but an option for caching a radius around you or the city centre would be cool.
I second multitasking improvements too. I think the interface for changing apps (at least on iPhone3) is more suited to those who think before clicking than those who want to quickly switch between things on the fly.
Freude, schöner Götterfunken Tochter aus Elysium, Wir betreten feuertrunken, Himmlische, dein Heiligtum! Deine Zauber binden wieder Was die Mode streng geteilt; Alle Menschen werden Brüder, Wo dein sanfter Flügel weilt.