Last week I had an interesting discussion with Sam Curren where we hit on the notion that the smartphone is a prototype personal data store (PDS). If you think about it, a smartphone--be it Andriod, iPhone, or one of the new Win7 devices--provides a common calendar, a common address book, and common photo library (among other things) with APIs for interacting to all of them.
For example, I can change out my calendar app to something like Calvetica (a popular alternate calendar for the iPhone). Doing this doesn't change the underlying calendar data or interfere with any of the other tools that use and access the calendar. Everything else still just works the way it always did. I simply have a different interface.
Or, I might download a new app that uses my calendar and adds things to it. Again, everything else that uses the calendar is richer and better because there's a new actor playing with my calendar.
Of course, programmers are shaking their heads and thinking "duh! this is the way things are supposed to work!" and that's true. But this is a watershed moment for Joe User. Smartphones are training people to think of the calendar not as an app, but as a data service that multiple apps can interact with. They might not use those terms, but the intuition is right. This is the kind of understanding that we need for people to really get the full impact of a PDS.
On the other hand, one of the dark, dusty corners of the "smartphone as protoPDS" idea is syncing. A true personal data service won't be one place where you keep data, but a service that manages data from lots of places. IMAP is a start at this idea, but syncing data across multiple devices is still an ugly stepsister to the flashiness of the whole smartphone idea. I've got MobileMe and I'm not very impressed. Its surprising that Apple hasn't done a better job on this front since iTunes is such a spectacular success at mixing stuff you load in the app with stuff you bought (and really maintain) somewhere else. There's much work to do here.
The Kindle system is another example of an app that does an admirable job of mixing cached content with a service that manages that content across multiple devices. The problem with the Kindle system is that it's closed. I can't write different apps that use that content and upload new content.
Still, with all their limitations, smartphones seem like a conceptual model for how people will interact with their PDS. A true PDS is a richer, more flexible, and full-featured version of the data repositories, services, and APIs that exist now in the thing you carry around in your pocket.