i was wondering about this as well. my paradigm dealer suggested it when i picked up my system,but i was wondering if there's really a big difference...
Bi-wiring is something that splits a group of audio nuts right down the middle. Some people claim that they hear a difference, others are the exact opposite. I personally don't notice any difference at all. If you want to try it, use some generic speaker wire to see if you hear anything diferent. Don't get suckered into buying a specialty Bi-wire cable if it won't make any improvement in your system. Just my $.02
Bi-wiring may have its most effect when you use thin leads and have long distances. Of course, the same effect could be achieved by choosing thicker speaker wires (gauge 12).
If the diameter of the wires is enough to make the impedance ignorable, the effect of bi-wiring is the same as connecting both sets of speaker inputs directly to each other - which is often the the default.
Another topic is bi-amping.... But if you're interested in that, you may want to read our primer on that subject.