Right now we record in mono using Marantz PMD670/PMD660s and Sennheiser 421IIs. In the past we have done two channel recording--i.e. recording to a stereo recorder (analog cassette, DAT and MD) by splitting a mono mic signal between the L/R stereo channels, and have used two channel recorders to record two individuals with one voice per channel, but we have never done true stereo recording.
From what I see, true stereo recording unusual in this field.
I know some ethnomusicologists and folklorists who use a single-point stereo mic as their "go to" mic for both music and interviews, but that seems to have as much to do with really liking a particular mic and not wanting to haul too much gear around as it does a desier to record interviews in stereo.