I tried it once when I first started out of curiosity and it was very soft. I don't remember if it got DOS or not. I like soybean as part of a recipe, but not as the whole thing. I usually use 16% and have no problems at all with DOS.
A little bit of soybean oil can add a nice silky quality to the lather. If you keep it at less than 15% and the balance are stable oils, it shouldn't be too DOS-prone. I don't use it any longer in my formulations but it has a place. I've given up on rice bran oil too (for soap) as I prefer olive oil and it's one less thing to measure out and store. I like rice bran for lotion, however.
Well that is true. I have been using soybean oil in every recipe, but in combination with multiple oils. I haven't seen any DOS in any of my cut soaps. Then again they are fresh. Time will tell, butthey will be used by then!