mike is right, all the plugged in items in a house draw power and it does add up. This is called the "phantom load". If you're going away for more than a few days, it's a good practice to unplug all those things (including TVs) that draw power in a standby mode.

PS - I think power supplies/wall warts that power electronic devices are theoretically rectifiers, not transformers. No matter, the "transformer" term is widely understood and used.

Older NiCd batteries DO develop memory, and lifetime is extended by not leaving them on the charger all the time, but charge, unplug, use, recharge. Newer NiMH batteries do not have much of a memory problem, so it doesn't matter so much.

One thing to keep in mind is the both batteries and chargers can fail and cause fires. Rare, but it happens. It's better to leave things unplugged.

Not enough to matter.

An unloaded transformer has a VERY small power dissipation.

Even the with a rectifier circuit on the output of the transformer, the capacitors charge up and the leakage is VERY tiny.

This whole thing is caused by some fool that measured the current without looking at the phase angle to the voltage.

Just like the 'power factor corrector' charlatans.