I have read several posts from users on the forum who have the Logitech K400 wireless keyboard and seen varying levels of success being reported. The http://elinux.org/RPi_VerifiedPeripherals#USB_Keyboards wiki page lists this keyboard as working, but there is no mention of the touchpad. This guy: http://wenlong.wordpress.com/2011/10/30/using-logitech-k400-wireless-keyboard-with-linux/ among others claims that the K400 works out of the box with Debian. My own keyboard works, but I get some sticky-keys and my touchpad doesn't work at all. When I try to reconfigure the keyboard, it comes up as a Generic 105-key, and (although there are a lot of logitech keyboards listed) the K400 is not an option I can choose.
If you have tried a K400 with your Pi, please post in this thread and vote in the poll to let the community know what your set up is, what level of success you've had, and if you had to work any Linux magic to achieve it. Then maybe we can come to some sort of consensus and update the Verified Peripherals page on eLinux, and avoid having people buying keyboards that aren't compatible. Perhaps we can also get a standard fix or set of instructions for owners of this popular keyboard.
My setup -
Distro: Debian “squeeze” 19-04-2012, with updated boot files (to fix SD card compatibility)
Power Source: HP Touchpad charger - 5.3V at 2.0A
Keyboard works: Yes, but with sticky keys
Touchpad works: No
Notes: Nothing in other USB socket.