Trouble is you never get a balanced debate on the dangers/merits of pot. On one side you have the converts, often hippies, on the other you have the 'straights' who have never even smoked it, so how can they possibly comment?
There is growing evidence to show a link between cannabis use and psychotic illness. I believe this is true. I had a psychotic episode followed by a breakdown 15 years ago, which I am convinced was linked to smoking dope. I now rarely smoke it. Sometimes I am ok with it, other times it makes me paranoid and jumpy.
As for the person who said 'no calories' as a good point about cannabis - what about the bloody 'munchies' it gives you, which makes you raid the fridge?? Thats another reason I don't smoke it - it can make you fat!