battery feedback loops
Along with the features that were demoed on stage, an iOS 8 graphic displayed some additional functions that went largely under the radar, many of which look quite interesting. For example, iOS 8 will apparently display battery usage by app, a handy feature that will let users monitor the battery drain of specific apps, shutting down those that are drawing too much power.
The product purist in me says "this is something that the user should never have to worry about. Why would any normal human ever want to monitor how much juice an individual app is using?" And herein lies the difference between want and need. Battery life isn't scaling with Moore, and knowing when you're going to need to tether your phone to a wall or a larger battery is something that has a real (world) impact on the life of the user. You don't want to know the details of how your apps are sucking power, but you need to know.
And I think this will also drive some market feedback around power consumption. Making this visible to the end user -- even if it's only the power user who pays attention (pun not intended but not corrected) -- will potentially drive power consumption feedback into app ratings. ("1 star, had to kill because this thing was KILLING MY BATTERY!!!") Developers will hate these reviews, but it could force them to pay more attention to power consumption. feedback loops in development tools are one thing, feedback loops in the market are another.