Generally, I've never given any actual written material to my friends, but verbally we do tend to talk alot about ideas, especially in humanities-type subjects. However, during the assesment period I personally don't consider it worthwhile to help your competition along, especially when the top few ranks are like a bottleneck and are very highly contested, sometimes only half-marks separating each other. However, I have a couple of friends that I know won't beat me, but still work hard at it, that I always try to help out verbally with ideas and essay writing.
But having said that, there was a time when I was discussing ideas with a friend of mine about one of my major works, and the next lesson she went right along and stole my idea for the project. Ofcourse, there was a big uproar amongst my friends about it, so she ended up changing, but my point is you never know about some people.
Once you have you rankg and when it comes to the time of HSC exams, your results and UAI hinge on the performance of both you class and you within it individually, so as a class we have to do everything to do really really well, however, you personally just have to do that little bit better also. I guess this is the right time when you should share notes, ideas, study together, etc.