Ok so I booted my droid WITH the usb pluged in to the device and it would no longer charge (usb hooked to my PC NOT the charger) I messed and messed with it and nothing I did would help. I finaly pulled the batt. let it set for a min and re-installed the batter. I booted up WITHOUT the usb pluged in and waited for it to boot completly and it worked!!
So I decied to see if I could reproduce the issue and I could 100% of the time. IF your phone is OFF and the USB is pluged into the phone and THEN you turn the phone on you can't charge from the usb again untill you pull the battery (as I said above).
I only have my droid to test this on but I have read about people not being able to charge off of the USB so I thought this may be helpfull. Let me know if anyone has seen this issue or not.