Medically, it's pretty neutral.  It has positive and negative effects.  There are 2 primary strains, sativa and indica.  The sativa strain increases cerebral activity and creativity, and indica is the typical eat-food-and-lounge-around-weed.  The pot does have negative effects on your lungs and does correlate with schiziophrenia, but it also can be very useful in treating pain, ADHD, AIDS, and mental disorders like depression, abuse of stronger drugs, hapatitis, parkinsons, and bipolar disorder.  But for the most part, the health effects are pretty minimal.  The true pro-con comparison is whether or not it's worth it to you in terms of pleasure vs. legal hassle.  And since it's not legal, you have to make a choice.  As for me, I'm a pussy and so I don't smoke weed.  Also, it's notable that the negative health effects are minimized by using a "vaporizer", a device that lets you get the high and the THC without negative effects on your lungs.