There are a number of new features in iOS 6, some them are not really all that new, and not all will really be of use to the average developer. The number one feature that we should see making its way into the majority of app is the new Facebook integration available. And, of course there are all of the new tools that can be built to hook in to Apple's new Maps app.
If you're a developer, just head over to the Apple Developer Center to find all of the tools and software you'll need to get to work.
source: Apple iOS Developer Center