I think there is alot more then that, I know for example that some mobile phones brands include very sophisticated noise reduction alghorithms, and I have to say I can really hear the difference when speaking with someone who is in a noisy place.
For what I know anyway they are very complicated algorithms, and even proprietary if I recall right.
I just throw my 2 cents, but I have never done anything like this, how about 2 microphones at, for instance, 90 degrees and then make some sort of difference of the two signals? This assumes that one guy is speaking from near and front of you and the noise is more distributed in the ambient (coming from more far) so it would affect in similar level both mics ? Or maybe then not...but could be tested.