Linus Torvalds has already pulled in Greg Kroah-Hartman's staging tree for 3.9 per this pull request. There's quite a lot of changes in store for this area of the Linux kernel where new, early Linux code lives until it's ready to be officially moved elsewhere. While there's new drivers, some drivers graduating from the staging area, and various clean-ups, overall the net number of lines of code changed is close to neutral.
In going through the massive staging driver change list, among the highlights include staging drivers for Google's Goldfish Emulator (there's already been pulls elsewhere affecting Goldfish for x86 platform, audio, etc), a QEMU pipe driver for Goldfish, OMAP5 support has been added to Texas Instruments' OMAP DRM driver, there's quite a lot of Comedi driver work, some drivers have graduated from the staging area, the usual XGI frame-buffer driver work, and a fair amount of BCM driver activity.
Among the brand new drivers are drivers for accelerometers, gyroscopes, and magnetometers from ST Microelectronics. Another new Linux staging driver is for the Invensense MPU6050, a gyroscope + accelerometer motion tracking device.
Overall it's another exciting staging update for the Linux 3.9 kernel with new hardware support continuing to be added to the Linux kernel, especially when it comes to hardware components affecting mobile/embedded devices.