They decriminalized it here in Massachusetts about 2 years ago, $100 fine for up to an ounce. Problem is it doesn't really change anything unless you're on your own property, with no paraphernalia. If you're not on your or someone else's private property (with them knowing) then you're "possessing in public". If you have any paraphernalia, that's been used (a bowl with some resin, or a pack of papers that's not still sealed up from the store) then they can get you with public intoxication since there's no way to test on the spot for being stoned (thanks to visine and careful acting) it's considered acceptable for a cop to just assume you're stoned if you have any evidence of smoking before.
Then if you have it in your car, they can get you for trafficking, if you have a bowl with some resin in your glove box, instant DUI exactly the same as being pulled over with a beer in your hand.
Then there's the other issue of that the decriminalizing and subsequent fine for small amounts is a state level thing, but local municipalities can still add their own bylaws. For example, in Massachusetts the state law says that up to one ounce with no paraphernalia or other evidence of recent consumption is a $100 fine and forfeiture of your bag. The thing is that the majority of towns in this state have enacted their own bylaws with their own fines, Framingham for example has a $350 fine added to your state mandated $100 fine so suddenly you're getting fined $450 for a $30 eighth.
Some of the towns even have other stipulations as well such as not being allowed to purchase property in that town after being caught in that town, etc.
Then remember the school zones where this decriminalization doesn't apply, if you're pulled over within 2000 feet of a school and the cop smells your bag, you're being arrested just like before this law went into effect.
It's nice to see the state pretending to be compassionate, but really all their looking for is income from fines. Even if you play by most of the rules, a cop is still gonna think of anything he can do to arrest you, so it really doesn't change anything other than having a fine to pay that's due before you can come up with the money you owe to whoever bailed you out.