Yo riot! Pairs of more or less identical mics are often used as a "coincedent pair", also called X-Y. The two mics, generally cardioid or supercardioid (not to be confused with hypercardioid, which is a different animal) are placed like a letter V with the 2 capsules at the point of the V, as close as they can be to each other without touching. The angle usually varies from 90 degrees to about 120 degrees, depending on how tight the mics' polar patterns are, how far they are from the source, and just how huge the source is. The two mics need to have very similar output across the audio spectrum, so you don't have spikes in one side of the stereo image at certain frequencies, hence the need for a matched pair.
Ideally, the 2 mics' pickup fields overlap, like the 2 fields of view of a pair of binoculars, and when brought into focus, create a stereo image, like your eyes (or ears). You can use this effectively to capture larger sources that have different sounds coming from the different parts of them, like a guitar or a piano. X-Y can also be used at a greater distance to capture larger sources, as in live recording a stage, overheads for choirs, stage musicals, or as drum overheads. Hope this helps to make some sense out of it.-Richie
