Jibult,
Researchers have demonstrated that THC ingestion decreases SWS and REM sleep, and has sometimes been found to eliminate REM sleep altogether.
Use and withdrawal do not disable REM sleep altogether, but it has been clinically shown to greatly decrease the occurrence of these two stages of sleep.
This is WRONG (as is most of this misinformation). A human cannot live past ~6 days without REM sleep without losing sanity and most bodily functions - and this is NOT why you do not remember dreams. Smoking cannabis does in fact reduce REM sleep - so you are right a bit (again), but not entirely.
The remembering of dreams have primarily to do with your CB1/CB2 receptors being flooded with electric action potential traveling down your axon to your dendrites towards your hippocampus, where they are bound (turned chemical), which greatly reduces short-term memory. Keep in mind this is far from the only location of such receptors. There are still many ophan receptors that have to do with REM sleep, and we still don't know much about it.
When you smoke and sleep, your short term memory is pretty much shot, hence the inability to remember vivid dreams. OTC supplements like Melatonin, or prescriptions that contain GABA (a precursor to many chemicals, i believe even dopamine, norepinephrine, serotonin, etc) also can help with your seemingly dreamless sleep.
^ That is a very simplistic/basic/loose, semi-right explanation... Didn't want to turn this into ADD material. If you are really interested, psychinfo and psyc database has a lot of great research regarding REM sleep and cannabis. It basically inhibits your stage 3 (REM) sleep due to several factors, but it doesn't prohibit it at all.
Cannabis does not cause physical addiction. Technically you can get addicted to ANYTHING, but there is nothing in the plant that specifically causes you to want it more.
This is also wrong, though only slightly. Cannabis CAN cause slight physical addiction - but the W/Ds are laughable compared to nearly any other illegal substance besides traditional psychedelics. Heavy smokers who quit "cold turkey" (if such a thing is even existent in regards to cannabis stoppage) do experience very mild symptoms, such as hunger depression, weight gain, and phantom pain in MMJ patients... however, cannabis is primarily a psychological beast. Again, semi-correct, but on the right track.
I guess I was pretty right in my guess that this thread would be filled with semi-correct information. At least there are plenty of lulz to be found here. Most of this can be found via our very own search engine.