If your Aluminum Apple keyboard suddenly tells you it can't power a USB device anymore (that it once did power without issues -- WTF Apple?!?), try unplugging the keyboard for 30 seconds and then replugging it. My SD card reader works again after doing that, though the LED no longer lights up. My Logitech camera (that once worked plugged into the keyboard) seems to not work anymore. I wonder if this was a change from Leopard to Snow Leopard?
Apple makes great stuff, but they'll just randomly change things sometimes, seemingly unconcerned with the problems those changes will cause to their uses. Rakin' frakin'...
Just had this problem on my late '07 Alu iMac. never had any bother before, it was always possible to have the wired MM and 5th Gen iPod attached. Today got a low power warning on just the iPod! (wireless MM now)
I unplugged it and reconnected after 20s - was all fine again. How odd.
interested on the power discussions here, the system profiler says the ipod is drawing 500mA thru the keyboard, and the keyboard itself only needs 20mA[From New Apple keyboard, doesn't sync or charge ipod nano - Page 5 - Mac Forums]