The iOS SDK is well documented, and generally allows for relatively easy creation of stable applications within the iOS ecosystem. Compatibility across devices is ensured because there is no fragmentation in the iOS ecosystem, except for between iPad and iPhone/iPod Touch apps, but there are specific API's in place that allow for Universal apps that work across all devices and are formatted specifically for each device.
Room for Improvement:
My major con for this is that it's Mac specific; if you don't own an Apple computer, you cant (legally) develop for iOS, which is incredibly small minded of Apple. Also, Objective C would not have been my first choice of a programming language if it had not been forced on me by Apple, I prefer C or C++ in comparison. Even Visual Basic is easier to code in.
As a Mac user, I was lucky enough to be able to develop for iOS on my device. Unless you can afford the Apple premium to buy an Apple computer, you can't really develop for iOS (legally at least), which is a definite con. All in all however, the iOS SDK is very fleshed out and full of thousands of useful API's that you can use when coding applications for an iDevice.