Electrical tape has a large number of uses that are neither unique to electricians or members of a marching band. Electrical tape has a strangely low profile with regard to popular concepts of what's useful for a household, far outstripped by duct tape, even though I have found the former far more useful to me than the latter.
Duct tape is reasonably effective at sticking things to things and making them stay stuck. However, it is wide, it is not smooth, and it weathers badly: it loses adhesion as it ages, or if water creeps in under the adhesive. It has excellent tensile strength, but either requires scissors to cut or is vulnerable to torsion damage (to be easy to remove from the roll). Duct tape is a reasonable adhesive, but it is poor at tasks not fundamentally related to sticking something to something else.
Electrical tape is much the opposite. It peels up, but it is no more prone to doing so after a year than after a minute; it is highly stretchy; it is easy to snap, but it is not prone to being damaged by a sideways pull or a twist. It is surprisingly poor at sticking things to each other, but it is exemplary at many other tasks.
I've occasionally used electrical tape for variations of its usual purposes. The sound cable I use to connect the audio jack of my laptop to the television has no strain relief, so I've wrapped near each plug with several layers of electrical tape; half a tape-width out, fewer layers; an additional half-width has one layer. The result is a cable that tends to bend smoothly instead of kink, improving its reliabilitly. The other traditional use I've had for it has been to patch over damaged insulation on the cable for my old earphones.
The most important use, however, has been a replacement for the rubber spacer under the bell on my bicycle after the previous one got knocked loose during a crash. A larger amount of tape was used to similarly increase the thickness of the crossbar of my roommate's recumbent bicycle (before it was stolen, anyway), which was otherwise too narrow to mount his headlight on.
We are trogloditic in our video game console system choices, so we only have one platform (a Wii) that uses wireless controllers. All of our GameCube controllers are different colors, and the plug color matches the body of the controller, but our XBOX and Playstation 2 controllers are not so easy to tell apart at the console side. They've all received stripes of varyingly-colored electrical tape, with matching stripes on the plugs, and now we immediately know which port each controller is plugged into.
My toaster oven caught fire earlier this evening as I was preheating it for cheap pizza. I had already been planning on replacing it with a standard toaster as we're using a George Foreman grill for our hot sandwiches now, and this probable damage to the liner is enough to condemn it. It is now sporting a bright red X of vinyl tape, and will soon be exhibiting this decoration in an electronics recycling facility or perhaps a middle school science class.
Electrical tape is catastrophically underrated; the only conclusion I can draw is that duct tape hired a better advertising agency.