I've been in a plane that landed-out on a plowed field - in a SGS 2-33A on July 26, 2008. I was a student pilot, front seat, with CFII in back seat. CFII was short and couldn't see the altimeter or airspeed indicator from her position. We were towed north from OG48, a grass field in Oregon. Had a pretty good head wind. Plan was for a simulated rope break at 200 ft, then circle back to land. Not an impossible turn for a glider. Anyway, I released a bit higher than planned. By the time I turned us around we were high and in close because of the headwind, which was now a strong tailwind. My attempts at slipping were still hesitant and sloppy. We were not going to be able to land at the takeoff field. The CFII took over and had me call out the airspeed while we overflew the airfield and landed in the plowed field south of Herman road. There were a lot of stubbles left on the field but in any case we landed OK. We could be seen from Interstate 5 and nearby roads, so we stood near the glider and tried to look like things were OK. Occasional smiling wave to a passing car. No point getting the authorities involved. We eventually got the glider towed back to OG48 behind a lawn tractor with the CFII and myself supporting each wingtip.
I'm not sure there was much to learn from that episode - other than at no time was I frightened. A couple of my thoughts were "This should be interesting," and "ha, don't think a go-around is a possibility!"