In the latest beta of iOS 6, Apple has included a feature coined Wi-Fi Plus Cellular. The surprisingly blandly-named feature allows apps having troubles with Wi-Fi to switch over to cellular data on the fly. This addition aims to smooth out spotty Wi-Fi signals or access points with poor quality Internet connections but supplementing trouble spots with dual-connectivity.
Wi-Fi Plus Cellular can be found under Settings > General > Cellular and allows users to toggle the feature off or on as desired. This preference pane also allows fine-grained control over individual apps as well, namely iCloud Documents, iTunes, Passbook Updates and Reading List.
It's unclear if other apps could appear under these settings as well, similar to the notifications panel, or if Apple intends Wi-Fi Plus Cellular to apply exclusively to those apps. The latter seems unlikely to me, but warrants consideration.
Additionally, AppleInsider also notes that WiFi Plus Cellular will apply to FaceTime, Apple's semi-proprietary video conferencing standard, in order to avoid dropping FaceTime calls. Curiously, this feature won't be available on the iPhone 4 -- it only seems to be available for the 4S.
Also in the latest beta, Apple has slipped in a new featured named "Bluetooth Sharing". The addition will allow apps to share data via -- you guessed it -- Bluetooth. Interestingly, with Bluetooth Sharing enabled, apps can share data even when they are not in use. Apple has been a notorious stickler when it comes to background processes, so this is a intriguing inclusion by Cupertino.