Duct tape (or "Duck Tape", I'll get to that part later) is considered to be almost magical in its applications.

"Duct tape is like the Force: it has a light side, a dark side, and it holds the universe together." -Unknown

"There are only two things you need in life:  duct tape and WD-40.  If it moves and it shouldn't, use the duct tape.  If it doesn't move and it should, use the WD-40." -Unknown

"Duck tape" was invented around WWII - soldiers needed a strong adhesive, and "duck" tape had another useful property - water rolled off the surface, akin to a duck's feathers.  After WWII, it became widespread in ducting (AC/heating applications), and gained its classic gray color that we all know and love.

Duct tape has been used for just about everything - books have been published on the subject.  There is even a scholarship that offers college money to couples who dress entirely in duct tape for their senior proms.  Duct tape purses were a brief fashion trend a few years ago (this being written in 2008), and some still hold that fashion to this day.  I once knew a man who built the chassis of his car from steel rods and duct tape. 

Duct tape is the "emergency fix" for just about everything.  Even when electrical, gaffers, or another type of tape would work just as well, we default to the mystical duct tape.  It has been used to hold aquariums together, plug holes in boats, serve as temporary door hinges, and even as a way to protect a house from radiation (although this didn't work out so well in the end).  Basically, if it moves and it shouldn't, use duct tape.

I guess the maxim "you can fix anything with duct tape" holds somewhat true - its wide range of uses and versatility make it preferred over other adhesives, even when the other adhesives may do a better job.  I suppose that keeping a roll of duct tape is better (to some people) than keeping five other rolls around for different uses.