i took the Kaplan class and have been teaching for them for the past 3 years. from my own experience and feedback from students, i think some strategies are helpful and others are not useful at all. i try to be pretty straight-forward with my students about what strategies are worth-while and which aren't....
i suggest that the maping strategy is less important during the science passages, but can be very helpful for the verbal....mainly for the reasons that johnboy12 gave. you CAN'T expect to be a pro at active reading/mapping overnight. your teacher should have given you the analogy about learning how to type properly....you are slower at first, but with practice you find that it is more effecient than using 2 fingers. with that said....you HAVE to practice the strategies consistently from the beginning of the course (during practice materials, tests, etc.) right before the REAL test, i tell my students that if they haven't been practicing the strategy, then it's way too late to start using it now. also, don't forget that an important component of the mapping strategy is also the active reading....asking questions to yourself about what the author is trying to say and anticipating where he is going with the passage from keywords, language, etc. this was really hard for me to master, but i can say with confidence that it helped me anticipate potential questions and is part of the reason i got an 11 in verbal.