Any effects on the brain will be short term (as far as mood goes) Now I have heard from a number of credible people, all of whom are unbiased, that marjuana will effect long term complex mathimatical skills. Meaning higher end math will be a bit harder to grasp. But im not too sure about those claims.

Lungs are really the only other concern. But dollars to dildos your heart will give way before your lungs ever start experiencing problems. You need to be a 20year+ smoker for any form of cancer.