Not had the time to read the whole thread, but I'm guessing we've had the haters, the current users and the semi-supportive ex takers.
I first tried it when I was 16, smoked it constantly since I turned 18, from the end of upper 6th through Uni (a 3 month gap last year), I have at least one a day.
I have experienced very few negative effects - if any, I find it helps me concentrate and focus on things - which is very rare in people who take it from what I've experienced.
I stopped for 3 months last year, which I did as a kind of controlled experiment to see if it had effected me in some way I hadn't noticed while still using it, I went to about 20-30 ciggies a day (high pressure time of life), and would have a lot more alcohol, to start with I lost about 1/2 a stone (back to 12) as my metabolism sped back up to its normal rate (Cannabis speeds your metabolism in the short term (munchies) but over the next 12-18 hours will slow it down - this is why some stoner's gain weight - the overall slowing of their metabolism, not because they've always got the munchies, though some people vary).
I dropped the half stone in about 3 weeks, but quickly put it back on again through alcohol, ciggies, etc and went to 13 & 1/2 stone by the end of the 3 months.
Over the period I feel my ADD worsened, the alcohol I'd started to consume and the ciggies ruined my skin and for the first time in my life I actually got sick (first time I'd seen my doctor since my jabs when I was a kid.). I didn't feel any negative effects or signs I was mentally addicted (physical addiction isn't possible) and felt happy that with the kind of life I like to lead Cannabis is better for me than the alternatives of alcohol and cigarettes (Though I do enjoy the occasional cigar!). Without cannabis I found myself going out more and more (till 2am most days) and socializing in different circles, circles that were generally more pretentious, a bit more plasticy and in places that I was more likely to find myself in trouble.
At the moment, I typically have a rollie when I get up, the same at lunch, I then smoke bud when I get home. Weekdays I have a 7 O Clock rule which I stick to religiously, at the weekends I generally won't smoke bud till around 2 – 3 in the afternoon (typically when you could crack open a beer). I dropped the weight I gained relatively quickly and have stuck to the exercise routine I've recently started – not been ill or had a day off sick either, still smashed my targets to bits, got my bonuses and 2 pay rises so I think its safe to assume it doesn't effect my work. I have about 2 beers a week – but that's it for alcohol.
Without cannabis I'm an impatient dick who dresses badly, drinks in all the wrong places and generally achieves less day to day.
With it I'm calm, collected, and doing well for myself. Its not the same for everybody – it depends how your brain works. I still dress badly though.
Decriminalise but keep a sharp-eye on it I say, punish the groups of chav scum who sit outside schools and in parks, or who walk round town. Don't punish the guys who sit at home, grow enough for themselves who won't go out and make trouble, the guys who light up for the walk home from the night bus, or the guys who've just had a rubbish day at work.
Common sense is all that required.
(my sarcasm sneeking in) 
