I was thinking about how Daniel said that his guitar sounded "almost like there is a chorus on it." I think I know why.
Many subwoofers have what I believe is known as a "bass reflex port", or basically a hole which allows all of the speakers movement to be utilized to create a bigger sound. When a speaker moves, it pushes a compressional wave forward, out toward the audience. Then it must retract, or reflex, during which time it pushes another longitudinal wave (same as compressional) in the opposite direction. This sound can be harnessed by a bass reflex port, pushing sound out, and essentially making the speaker sound louder and fuller.
An interesting side effect of this, however, is that the wave created by the reflex comes slightly later than the original wave. The sound created by the reflex is actually 180 degrees out of phase.
A guitar operates on the same principle, but to a much more dirty effect. The top vibrates like the speaker, but the back and sides do too, so every sound played by a guitar naturally has a bit of reverb on it and much of the guitar's sound comes to the listener, out of phase (in varying degrees).
A chorus effect does just this. It splits up a signal, and pushes part of it slightly out of phase from the dry signal.
Having an extra soundhole in the guitar allows more of the sound from the reflex of the guitars top to exit the guitar rather than being absorbed, creating a chorus effect.
The effect would be maximized by placing a soundhole on the back of the guitar. However, since most people cover the back of the guitar while they play, it wouln't work.