There seem's to be an second problem with the USB devices which could be related to the firmware/OS distribution you use. My R-Pi works well with the Raspbian distribution (taken form here: http://www.raspbian.org/PiscesImages
, but with the current Raspbmc or Openelec images the R-Pi doesn't recognize any keystrokes or mouse movements.
The hardware configuration is always the same: power supply 5 V/1,2 A, Logitech MK 210 keyboard/mouse set (USB transmitter draws 55 mA). The voltage on the boards (TP1 to TP2) varies between (only) 4,65 and 4,7 V most time (with an without USB device or ethernet cable), but Raspbian works smoothly as said above. There's no significant difference between the different distributions.
My experiments with other configurations (cabled keyboard/mouses, powered USB hub) didn't change anything.
Maybe one of you those with the keyboard problem could test the Raspbian image and report here?
Greetings from Stuttgart/Germany