Hey, glad to hear I'm not alone...
I've been experiencing crazy pixelated visual snow, flashing lights, colored dots, light tracers, and after-images of contrast colors for about five years now, and I know with fair certainty its because of (or at least exacerbated by) marijuana use. Actually the first time I recall any visual disturbance at all was after the first time I rolled on ectasy, but its difficult to say what the real cause was because it was right around the time I started smoking weed frequently. Anyway, I haven't rolled in more than three years and I find my visual snow is related to my frequency of marijuana use, although it doesn't ever completely subside even when I quit smoking for a considerable period of time, at which point I found it to also be highly stress-related. (So to hell with not smoking

Anyway, I'm usually not bothered too much by it because I've gotten used to it, but sometimes it still gets really bad. Stress and caffeine make it much worse. In fact before/after test cramming usually (which entails ridiculous amounts of both) it can progress to the point where I see patterns and faces and odd tesselations of the strangest things spiraling out from the center of my visual field when I close my eyes. Which really sucks when trying to fall asleep and seeing scary faces is never fun (but always interesting).
I know that these visual disturbances relate to serotonin or similar neurotransmitter disturbances somehow. When my pixels get so bad I can't concentrate/get anxious/convince myself I'm going blind, I find that taking some form of flouxetine (prozac, etc.) once or twice a week for a few weeks really helps get it under control. Another interesting thing to consider is the odd and unfortunately understudied relationship between serotonin and psilocybin. I love mushrooms because when I trip, my visual snow goes away completely. (Of course, it's replaced by far more enjoyable visuals

But compared to real tripping, my pixelated vision just feels like some sort of constant unpleasant migraine aura, and at its worst, is accompanied by a headache. Interestingly enough, that actually may be the case, because migraines are also related to serotonin and other neurotransmitters that are disturbed by marijuana use in prone individuals.
I find my visual oddities interesting for the most part, even though I sometimes despise them and feeling like I'm tripping all the time can be debilitating in some situations... (driving at night, which I have to avoid.) But... it definitely puts life in an interesting perspective.
Hope this helps!
PS: I'm generally affected much more quickly and deeply by most drugs that I've done than most people I know (with the exception of cocaine and booze). Even after six years of heavy marijuana smoking (at some points extremely heavy) I still get instantly high after a hit or two and rarely build up much of a tolerance. Which is good I guess. Because its cheap

But the tendency for my brain to respond so well (or so badly... subjective judgment) to chemicals I think has a lot to do with the visual disturbances. Also, quite severe neurotransmitter imbalances are known to run in my family.