Two bad USB ports
Three week old i7 MacBook Air. USB ports worked great until a few days ago, then the left went out, then the right.
I returned it to Apple Store where they replaced it after determing that the USB ports had bent pins.
I have had Macs/PC's since before there were USB ports, so I know how to use them.
The tech suggested it might be the device I was plugging in that ruined them but I pointed out to him I thought the device was bad so I plugged it into my iMac where it works great.
So two thoughts, either the ports were misaligned inside the housing or they are weaker than past.
Additionally I guess it could be a fluke and won't happen to me or anyone else ever again.
Just wanted to post this as info or to see if a theme develops with these ports.
If your USB ports don't work, get a flash light and compare theme to another computer.
Had this been a Windows laptop I probably would have been told it was my fault and been out $500.
Apple's are more expensive but you get what you pay for, world class support along with a beautiful machine
iMac, Mac OS X (10.7), i7 12GB RAM