Gizmodo: While you might think that all miniUSB cables are created equal, just because a charger fits your device doesn't mean you should use it. Different smartphones and tablets have different volt requirements; too many volts from the charger and the gadget fries, too few and the device will take forever to charge.
A recent example? While an iPhone 3GS and an iPad 3 share a 30-pin connector, their chargers output at entirely different rates. Mixing and matching won't be ruinous, but it can lead to frustration.