I just recorded/produced a whole album of songs w/guitarist playing acoustic guitar as bed tracks.
1) SM57 pointed at the 12th fret @ 45/angle (rear of mic pointed away from guitarist), about 5" from the axe
2) LDC hung above the lower body of the guitar, pointed down towards the sound hole, about 12" from the axe
3) Panned hard L/R
Everyone very happy with results; YMMV.
My brother Kurt was the guitar tech on the Godsmack acoustic EP, and related this tip:
1) Hang LDC as described above, panned centre
2) Hang two ribbon mics (Royer 121, 122, et al) above the guitarist's shoulders, panned L/R
I haven't tried that one yet, but hanging the LDC mic ABOVE, not below or in front of, the guitar seems the status quo for good sonics. I know I've experimented with LDC placement in front of acoustic gtrs, and it seems the only sound I ever like is when I've got the LDC above the guitar by about a foot or two, pointed down at the sound hole.
Happy hunting...