Touch. Deep integration with touch. As you see with the release of the Magic Trackpad, Apple is retiring the traditional mouse paradigm and moving on to versatile and complex gestures to aid in window management. Four finger swipe for expose and show desktop has been godsend for productivity, as has three fingers up and down for switching between h/m files in xcode. Let's not forget swipe to go back and forth in browsers, pinch to zoom, rotation, etc... None of which is possible with the standard mouse.
And peruse through Apple's touch gesture patent library and you will see that they haven't implemented a fraction of what they have patents to. You have neat stuff like three finger pinch (possible to close/hide a window, save), non-adjacent finger scroll (ex. thumb and ring finger, note that Magic Trackpad is big enough for this one, but existing options on MBP are not), and several others involving rotation and unconventional finger combos. Expect for these gestures to be baked deeply into the new iMovie, iPhoto, and iTunes. Seriously, can you imagine alternate paradigms for simply grabbing video from a bin once you account for different numbers of fingers involved in the drag?
A preview of Lion with these features will allow them to sell the next generation MBP with a new, much larger trackpad to accommodate the new focus on touch and touch gestures. If Apple scores a hit with this new focus on touch, it will be another competitive headache for thin, underpowered clients that serve up web content and can't handle advanced video and photo editing, not to mention lack large surface areas for touch gesturing.
What's in it for Apple:
If you think about this from a competitive standpoint, most of Apple's competitors want to lift computing into the cloud--Google with Chrome OS, HP with WebOS, and even MSFT with Ballmer's pronouncements of "cloud speed". Apple's strategy, and profits, are vested in adding weights to computing to take advantage of powerful, local, GPU and CPU intensive tasks, thus slowing, or even reversing the shift towards browsers and web applications, in keeping us grounded in powerful, local machines. If Apple finally figures out a way to get your mom editing video with powerful and intuitive new touch gestures, how is a web application going to respond to this from the confines of a browser? How is Microsoft going to coordinate with clone makers to agree on standard sizes and performance of computationally complex multi-touch trackpads? Touch and media editing all the way.