For a long time, chain whips have been designed like this:
Park Tool chain whip
You use this to get a good hold on your cassette so you can loosen the lock ring. Without this handy tool, getting your cassette off is downright impossible. Park Tool has come out with a new design for the tool:
Park Tool chain whip pliers
With this design you don't have to wrap the chain manually, you can just grab ahold of your cassette and go.
I know what you're thinking - how much time does this really save? Well, probably not much, but if you're looking for the cleanest way to work on your cassette, this is it. If you're looking for the biggest hassle when working on your cassette, check out the home made jobs below:
From a cut up crank arm
Some pipe and chain
Copper pipe and chain
Truly necessity is the mother of invention!