I certainly don't maintain that cannabis robs everyone of motivation. Only that it did that with me. That was very much my personal finding with weed. And I suspect that that depends on what strain people are using, too. For instance, the weed I smoked with my sister last summer was Indica-dominant, which is known to cause the unmotivated couch-lock syndrome. It certainly did that with me. In her case, that was perfect. It relaxed her, relieved some of her physical pain, helped with the nausea, and improved her appetite. It made me hungrier than normal, too, and made me mostly want to lie around and giggle and do little else.

As far as IQ depletion is concerned, I think that's a side-effect that varies from individual to individual, too. Storm Crow and others have posted threads in the medical area citing studies that show that occasional use doesn't seem to have any effect on IQ but that heavier users (defined as people who smoke more than five joints a week) can indeed show some indications of lowered IQ. In my case, it slowed down my thought processes, kept me from being as quick-witted as I normally am, and caused some aphasia, where I could conceive of what I wanted to say or write but couldn't actually articulate it. Since I was working as a professional speechwriter back during that time, that was a definite drawback for me. At the same time, I think it definitely spurred my creativity. That is, creative concepts and ideas came to me in new and noticeable ways, and I thought of several ideas for inventions and recipes during those toking periods. So that was fun.