First of all, there is no way a Pi will deliver 500mA to a USB port. You'd trip the F3 polyfuse before that happened.
At 100mA, you should be okay. The original versions of the board (Rev. 1.1) had 140mA polyfuses on each USB port. I still run boards of that version with mouse and keyboard with no problems. but I stick to simple, no frills, keyboards (no lights, no USB hub, etc.). Likewise, I use plain mice.
Best first suggestion would be to check the voltage across TP1 and TP2 to see if the Pi itself is being properly powered. Your Pi may have plenty of current to run and power the USB devices, but not enough voltage to keep them working.