iOS 5 is the latest in a great line of software updates for the Apple mobile devices. Beside the highly expected interface updates (new Notification Center, controls, etc.), lots of low level changes are taking place.
Paul was talking about the new Automatic Reference Counting (ARC) for memory management, iCloud storage, Twitter integration, storyboards, Newsstand apps, location simulation, airplay mirroring (iPad 2 only) as well as the new default apps and changes to existing ones.
Clipping is a handy way to collect important slides you want to go back to later.