Tom that cleared a few misconceptions for me.
"...there is already a city ordinance making marijuana enforcement the lowest law enforcement priority." Better not jay-walk then. My sister actually got a ticket in Seattle for jaywalking.

We've some draconian marijuana laws here. Individuals can have some serious penalties placed upon them for possessing even very small amounts. There was a measure passed a few years back that allows certain municipalities (not the state) to decide whether they want to decriminalize MJ or not- mine is one of them. So far this hasn't come up again so I think the powers that be have decided not to decide.
The ramifications are unknown at this point. Years ago I was discussing with my colleagues this very issue. I was concerned about how employers would deal with this. Many have post job offer screening followed up annually. My former employer states that they do so every year but never did. What they would do is UA anyone hurt on he job whether it was their fault or not. A person could have residue in their system from the weekend before- be innocently injured on the job via someone else's carelessness and subsequently have their reputation ruined, livelihood jeopardized and pay the medical expenses out of their own pocket. This bothers me.
I don't think it's unreasonable however, for an employer to expect their employees to show up to work and not be under the influence of intoxicants. The system that I've recently interviewed with proudly states that they are "nicotine-free" and that testing will be performed. They will not hire anyone who smokes or uses tobacco. I think these types of attitudes will persist in States that have decriminalized marijuana. Sure one can partake of it all they want since it is legal- but their job prospects may be slim if they can't show up without the evidence in their system.
Seems to me casual and small-time users will have little to fear from the Feds. It will be the growers and sellers who should expect to be prosecuted.