Why is there an arc when I pull a plug out of an outlet?
Whenever you have an appliance that is drawing current, and you pull the plug while it is in operation, you are going to draw an electrical arc. The voltage is high enough that current still wants to flow through the air to power the item.  This is not a good situation. Items that draw high amounts of current, ie; high wattage, should have an on/off switch in them to prevent this situation.  To some degree, it happens when you plug them in as well.

The effect is that you are burning the metal contacts in the outlets and the prongs of the plug.  As they become pitted and blackened, they do not conduct electricity as well, become highly resistive, thus creating heat and eventually will fail or burn up.  This is an unsafe condition.

The solution:  Make sure appliances are off before you plug them in or unplug them.  If you own an iron, then always set its temperature dial to 0 (zero) or "Off" before you plug it in or unplug it.  (Source:  Panasonic's "Important Safety Instructions" page).