I agree with Melissa; some people just dont want to stop because it's a ball.
I have smoked twice, both times to relieve my migraine headaches (hey, it worked!) but I have eaten it baked into brownies on average twice a week for the past three/four years. I don't think it's addictive for me, but I think it could be addictive for others, at the very least habit forming.
I've quit for awhile now though b/c it seems to have started having a negative effect. My blood pressure has dropped so low that I've passed out, I have complete laspses in memory, and I hate that "gotta eat" feeling.
All this hasn't made me a dummy though; just got my grades and I've got a 4.0 cummulative for my first year of graduate school.

Sorry, had to brag a bit; just found out about it.