As part of the HID (Human Interface Device) pull for the mainline 3.1 kernel is a Nintendo Wii Remote driver that makes it possible to use the Wiimote as an input device "out of the box" on future versions of Linux. There's also been additions to the sysfs interface for setting and reading the four LED states of the Wiimote, which can be used for other purposes.
The HID pull request can be seen here, which Linus accepted yesterday evening.
Besides the Nintendo Wiimote support, the Linux 3.1 kernel HID pull also has support for the Holtek Online Grip-based game controller, the Holtek Online Grip-force-feedback controller and support for the Speedlink Vicious / Divine Cezanne mice.
In the short time the Linux 3.1 kernel merge window has been open thus far, this is the only particularly noteworthy pull that caught my attention. However, the merge window is still going to be open for up to another two weeks, so in the coming days there should be more exciting reports. We know that still to be pulled will be major Intel Poulsbo improvements, a number of open-source graphics driver improvements, initial Intel Cedar Trail support, and various other changes.
For those hoping that the Linux 3.1 kernel will magically fix the power regression issues, it will not. So far I haven't seen any driver patches be pulled in that are setting the ASPM (PCI Express Active State Power Management) bits directly. Even if some drivers do, it will probably be a number of release cycles before there would be better driver coverage for knowing what hardware plays well with ASPM and which devices do not. Or the ASPM kernel code could also be improved to better detect when to actually enable ASPM (i.e. figuring out how Microsoft Windows is doing its ASPM detection), but so far the Linux kernel developers haven't yet figured that out. Nor do any of the changes happen to by chance address the power regressions I haven't yet documented in full.