I've done it, and I don't care if it's cheating. *MY* objective for taking calculus was to know how to use it to solve real-world problems -- not to memorize formulas, receive a grade, or outperform the others in the class. If I know which formulas to use, and I know how/where to find those forumulas, then I can apply calculus to solve problems. That was my objective.
So, I think if you look at it with that perspective (i.e.: it's not a competition between students to get the highest grade), then I think you can justify it.