Another new feature coming to developers next month and which we'll be the beneficiary of when 'Mango' is released in the fall, is database access.
Now before you groan with boredom, we should point that this little thing is actually quite huge--developers are pretty ecstatic about the addition. Why? Because now they can write apps that pull info from your contacts (read only) and calendar (also read only) and use them in their apps directly.
If you take the moment to watch the above video in a demo wine app, you can see how the augmented calendar works within an app (it both pulls down days and appointments), allows you invite people from you address book including their address, adds it to the calendar and then allows you to email all of it. Very slick. None of that can be done today, which is a quite a big hole in feature ability.
The slide below though does show there are limitations e.g. the read-only feature (which we think is fine) and the fact that Facebook is limited to contact name/picture and evidently Twitter will have no accessible user information (we're not sure why that is exactly). The point to take away though is that devs are very excited about this as it will allow them to create faster apps (less "pull from the cloud") with more robust features that are much tighter integrated with the OS.