lately i've been on a mid/side kick. but about 6 months ago i had a drum recording with only one room mic. just happened to be a ribbon doing the 'side' thing 10' back or so, but thats beside the point.
mixing i ended up panning it hard left and making a copy hard right, with reverse polarity. kinda like M/S but using the whole drum kit as the middle channel. just put it in there a wee bit and it made a nice ambient enchancment.
then i had a acoustic recorded both di and with a mic (cardiod, 12th fret, at sound hole, etc etc). was going to hard left/right these as the client had been doing, but it sucked. so... di up the middle, mic treated as the side channel. one left, one right flipped.
i think it sounded brilliant. not double tracked but still huge. could get it a few db shy of being the same level as the 'mid' channel without getting all phasey (great word, btw...) even down really low, it was way more dramatic than any mid/side mic combo i've done in the past. mess with sample delay on the di/mid channel and there is all sorts of fun.
anyhoo, i've been expanding on these concepts lately, but never really observed or read about anyone else doing M/S with things that aren't really M/S (mics in different places with non-standard pickup patterns with things that may or not be mic'd anyway).
best is taking a mono reverb, and multing to the two side channels, and putting delays with modulated feedback on both, with slightly off settings...
....wwwwwaaaaaAAAAOOOSSSHHHH!!!!--> --> -->
mmm... shoegazer never went out of style.