For me, hands down the best feature of iOS 7 is the new ‘fetch’ API enabled as part of the notification service of iOS.  Previously, notifications were a 1-way message, and I’m sure I’m not alone in wondering why, if the app has registered, and been allowed to send notifications, there wasn’t a way to send a payload with the notification to avoid the user having to manually get into an app to do an update.
The fetch mechanism allows an app to have a special wake state to download information based on a wake-up event triggered from a notification.  So hopefully, no more need to manually update Words with Friends just because a single person has updated their move!

I’m keen to test it out soon, and see what protection is in place to stop apps from abusing this service to download large portions of data.  I would have preferred a small payload to be allowed in an individual notification, as this would be less likely to cause users to have unintended downloads, but this ‘fetch’ method is more flexible for those hosting their own server infrastructure, so it’s a great thing overall.