It depends a lot on where you are in California. Some places are extremely tolerant. Some places you get the "Cletus P Coletrane" type cops who will cite you for driving under the influence or transporting,even with a card.
Generally speaking the local cops and government are ok with legal marijuana. The feds are not.
Luckily the federal harassment is slow to trickle down to the basic medical user,but they are busting growers and co-ops and harassing certain medical marijuana friendly Drs.You should be okay, though. Those cards carry a lot of weight around here.:thumbsup: