Ground faults! Ground faults! Ground faults! I am installing mine today. It doesn't quite relate totally to this topic but certainly worth a mention.
I don't care how many times you think to yourself, "if anything plugged in ever falls in that tank I will be sure not to grab for it". Low and behold the first time something falls into the tank...... Its just a reflex and I have been fortunate enough to get away with it a few times when I had my cichlid ponds outdoors.
They are not particularly expensive when compared to other things in this hobby and could very easily save your life or one of your family members lives. If you don't like the idea of installing them in the wall socket you can also buy in line variety for a few more bucks.
Not having them when you are involved with this hobby is like playing Russian roulette. Its just a matter of time.