After a recent trip, I've misplaced the wall charger for my Motorola Q. It's likely that the silly thing is just in a bag somewhere in the house, but my wife thinks it may be at her office. None of that really matters — the silly thing is missing!
Although I have a Motorola Q, which is powered by Microsoft Windows Mobile, I haven't used a Windows-based workstation in 3 years. I completely converted to Apple Mac OS X at that time. As if that's not strange enough, I'm a total Mac user, but don't own an iPod. This gets even weirder considering everyone in my house owns one, including my 4 year old son. Anyway, that was another mostly uninteresting digression.
As the title indicates, I was unable to charge my Q with the provided USB cable. After poking around a bit, I finally discovered that the device was configured to use USB for "advanced network functionality." I'm sure that's amazingly useful if your Q is fully-charged and connected to a Windows desktop. Disabling this functionality suddenly allowed my Q to start charging.
You can find this setting by following Start → Settings → Connections → USB to PC. Clear the "Enable advanced network functionality" checkbox.