It's no different from speaker wire in a stereo setup. It's all about the law of diminishing returns. When you step up from a Radio Shack cable to a consumer Monster cable, you may notice a difference, depending on the quality of your mic, pre, etc. This is due to wire gauge, soldering quality, resistance of the connectors used, etc.
If you're running a Radio shack mic through a Radio Shack cable into a computer you bought at Radio Shack, you probably won't notice much of a difference. ;-)
The biggest thing to keep in mind is that the only function a cable does is carry current from one place to another. The only time a cable will make a significant impact on an audio signal is when the cable is too narrow (small wire gauge), and you are trying to shove more info down the pipe than it can handle.
For me, I'll spend an extra $10-20 for Monster or BLUE, but that's mostly for the guarantee that they offer. That way, if it craps out on you, just bring it back. I'll personally promise that any difference in the sound that anyone can hear in a $120 cable is solely based on the fact that they want to hear a difference, because they spent WAY too much money on it!
-mg