Well, in those few areas of the country that allow for medical marijuana use, the fear was always that though the state or municipality allowed such use, the federal government did not. Theoretically then, the federal government could have come in at any time and penalized someone using marijuana medically, regardless of the safeguards or other laws in place.
But today, the dialog started to change on marijuana. Perhaps it's the realization that so many Americans support medical marijuana availability. Perhaps it's the fact that we are realizing the war on drugs is a crock. Perhaps it's the fact that we know there are bigger fish to fry and using government dollars to go after small time marijuana users just isn't worthwhile. Perhaps people are starting to come to terms with the fact that marijuana is actually less dangerous than alcohol and nicotine.
Whatever the case, today at least there's a little more breathing room (pardon the pun) for those with a chronic illness/chronic pain who use marijuana as a treatment option.