Just talking about the iPhone, there is an API that I’d like to see and I’m sure many applications would benefit from: A download manager. I imagine that an app could register to pull the content of a specific URL or the answer from a Web Service at a specified time or at specified intervals, and then the answers or most recent answer is ready for consumption when the app is started by the user.
Ideally, this would integrate with iTunes so that when syncing the phone, all the data-hungry apps get their mouths fed and are provided with the last version of the data they’re interested in. What I have in mind are news-plucking applications like All Things Digital or Bloomberg, or the TV schedule apps — or many of the other apps that you start, then wait to have their content pulled, and only then continue to use. The basic thing they do is simple: They all get their data in first. And I presume many, many of them in one or the other kind of XML application.
Man, would that improve my user experience of the iPhone.