The other problem with speaker wire is that you are likely going to be limited to one or two colors, mostly - if you're lucky. When you are breadboarding and prototyping circuits, you not only want to have multiple colors for the wires/jumpers, but you want to use and group them logically if you can (ie, use colors to represent what the circuit is connected to, etc - so you can trace functions by wire color).
For instance, say you were building an LED matrix display. You might use one color for the rows (drivers), and another color for columns; you could go further and connect up even rows with one color, and odd rows with another; do the same for the columns using two other different colors. If you do it right, it can make debugging a circuit less of a hassle.
The best source of wire for breadboarding and prototyping is 25 pair telecom cable; if you can find a long length of that stuff, you'll have the best set of jumpers and wires you'll ever want.