My experience has been similar to that of Roger&Me, that is, MMV (my mileage varies).
I'm a grad student who has been writing a research paper for the last week or two. I've been trying writing at night while "altered" on weed (complemented with sober writing during the day, of course). I think the key here is to get the dose right - if I get too high, my mind wanders and I feel like tripping out to music or something like that. At the right level though, I'm able to maintain focus on writing, while still having my thought patterns scattered enough to allow new ideas to float in, which I've found very helpful. I also tend to obsess a little more about my sentence construction and "phrasing", which may be making my writing clearer to understand. But, I do not plan to make a habit of this, because it's all too easy to get over the limit and waste the entire night. My will power is inversely proportional to the amount of THC in my system.
There was another occasion where I had a rather interesting experience with weed and studies. I was trying to read a paper that had some quite difficult technical concepts (math/robotics), on a Friday afternoon in the lab (sober). I didn't fully "get" the idea of the paper, and kinda gave up on it. That night, I got very high, and decided to read it again. My imagination was running wild, and I found that I was a bit slower reading it, but I could visualize all the concepts so much better. I completely understood everything the paper had to offer, and was even able to implement those ideas in the next week.
So my personal rules are - keep a low tolerance, don't get high and study every day, and if you choose to do it, try small doses, and you might find it beneficial. Of, course, YMMV (in very large letters).
