On the group snow run back in the end of January, we encountered a couple spots where the trucks in front had packed down the snow pretty well and with the low temps caused patches of ice. At one point in the trail, several of the trucks (including me) had to get up momentup to go up a small hill, lost momentum and slid backwards at a considerable speed. I had almost made it to the top on one attempt but got hung up on a rock and had to reverse out to try again, and when I put it in reverse and tapped the gas I started careening out of control backwards down the hill at probably 10-15mph which was honestly terrifying.
I took it out of reverse, put it in neutral for a second, then put it in drive and gave it gas to slow my backward slide knowing there were trucks and people back there. I was worried it would cause driveline damage, but I was more worried about hitting someone. Perhaps it was due to the extremely slick conditions where the lack of traction didn't cause binding, but I noticed no binding/banging/clanking or anything when I did it. It definitely did significantly slow my backwards slide and maybe prevented a collision.
My girlfriend looked at me afterwards and said she had never seen me that scared or move my feet and hands around the wheel and shifter so fast before!
Edit: here's a pic from the run