It is a very complx issue...
I my self smoke the herb occasionally, I'd say about once a week usually. Me and one of my friends usually blaze on the weekends. For me...it's definately not habit forming, I enjoy smoking marijuana but I am by no means addicted. I smoke when I get the chance and have someone else to enjoy it with. Sometimes I go a month or two without smoking, sometimes I smoke several days in a row. I have never felt any pressing urge to do it though, no physical symptoms of addiction.
At it's base level I believe there is nothing wrong with smoking weed. It's not physically addictive, and it isn't much worse for your body than drinking or smoking cigarettes.
I do agree however that it can still cause many problems. Often when looking to buy it, you will come across very untrustworthy and unsavory characters (although if mj was decriminalized, this wouldn't be a problem). Also for certain weak willed individuals it can become a habit (psychological addiction is another animal completely), and lead to them becoming a burnout/loser/waste of life. Plus, although I believe it's affects to be much less than those of alcohol when it comes to coordination, it's still dangerous to drive impaired.
I don't know whether it should be legalised or not, but I do know that I enjoy it. And when used in moderation and with responsibility, it is no worse a drug than alcohol.
Most wanted cars:
Ford GT, Aston Martin DB9, Nissan Skyline R-34 V-Spec II, 2004 SVT Cobra Mustang, VW Golf R32, TVR Cerbera 4.5, Ford Focus RS, Aston Martin Vanquish S
Still waiting.....Shelby Cobra, Shelby GR1, 2006 Ford Lightning, Next generation SVT Mustang Cobra 2006? Mazda Speed RX8