It seems like USB 2.0 hubs have a sort of circuit breaker functionality where if you plug a shorted device into one of the ports, the entire hub shuts down until power is removed from it completely. We had an intermittently shorting digital camera USB cable around here at work that was doing this to Macs and PC's.
You have to shut the machine down completely and unplug it's power supply, on a laptop this means removing the battery as well; a simple reboot will not fix it.
I guess with my MacBook Pro (non removable battery) I would be sol.
Two possibilities, neither of which are strictly recommended in everyday practice...
1. Let the battery drain to zero before recharging (inconvenient, and shortens battery life)
2. Reset the SMC (the last-resort option for correcting similar issues)
Info on resetting the SMC...
1. Shortens battery life? The last I heard, Apple recommends doing this once a month to calibrate the battery. It's supposed to help maintain the battery.