Smoked on and off for about 14 years and when I smoke daily I will not remember my dreams except maybe once a year I will remember one 'scene'...When I do not smoke I remember a lot more of my dreams, almost all of them.
I have a theory about this actually, since it has been found that canibinoid receptors are used by our body naturally without the aid of cannabis it was then found that the chemical produce by our brains which uses these receptors is used to forget needless information and organize our thoughts.
Now..When we dream in the state of dreaming of R.E.M the same kinds of things are happening...Our minds are forgetting and organizing memorys (such as: making predictions).
My suspicion is that there is a strong link between cannabis and dreaming.