In the power management pull request for Linux 3.10, PM subsystem maintainer Rafael J. Wysocki confirms the most interesting feature is the cpufreq driver for big.LITTLE.
Should you not be familiar with the big.LITTLE architecture, it's about pairing low-power processor cores with more powerful -- but more power-consuming -- cores. With the forthcoming Samsung Exynos 5 Octa SoC, the big.LITTLE design is implemented as a 1.6~1.8GHz Cortex-A15 quad-core design while falling back to a 1.2GHz quad-core Cortex-A7 when wanting to conserve power and not needing to do much work. Kernel work on big.LITTLE has been ongoing for a while and now there's a mainline cpufreq driver for handling frequency switching.
Another big change is AMD's frequency sensitivity feedback power-save bias.
Other power management changes for the Linux 3.10 kernel include a Samsung Exynos 5440 cpufreq driver, cpufreq core clean-up, cpufreq scalability improvements, cpuidle improvements, and Intel Lynxpoint LPSS (Low-Power Subsystem) improvements.