i don't have any experience with this myself, but i have a friend who claims to have learned something in a dream. he was always unable to roll very good joints. then, one night in a dream, he was rolling lots of nice ones. when he woke up, he tried the method he was using in his dream and rolled some very nice joints. this might be a different kind of case, though, since he didn't really get any new knowledge in his dream. instead, his subconscious just worked out a good physical method for doing something that he hadn't been able to do before.