And if you absolutely have no choice but to use a USB hub, then make sure it is an independently powered hub, rather than bus-powered. Bus-powered hubs are not permitted to supply more than 200 mA of electrical current to any single downstream device, and that's not enough to charge an iPod touch.
Independently active-powered hubs are permitted to deliver at least 500 mA of current to each downstream device, sufficient for charging an iPod touch.