[rick-slo]

A few comments after reading some of the other posts:
IMO
Stereo mic’ing on guitar can be done near field (close to the guitar) and usually is. Most solo steel string guitar recordings you hear were miked in the near field (within about 18" of the guitar). Spaced pairs may be done with completely different mikes with good results. For coincident or near coincident mic’ing similar mikes (perhaps matched pairs) are used. For recording guitar cardioid mikes are most often used. Omni mikes and further out distances may work sometimes but you need a very quite room with good acoustics. Most phase cancellation problems in spaced pairs are on the higher notes. I hear it most and phase correlation meter is furthest off around the fifth fret first string. That is where to most critically listen when spacing mikes. The low notes are relatively fine over a variety of mike positions. The three to one rule is often cited but it is really more apropos to mic’ing two separate sources with two mikes. In recording a single guitar the rule does not work out so well. There is an additional issue in that the guitar does not produce sound from a small localized area (point source) but from a broad area of surfaces which I think is at least in part why single mike recordings, in the raw state at least, do not sound very good.