Currently, 4 states have legalized marijuana for recreational use, and almost half the states in the country have instituted some form of medical marijuana program. Millions of patients and casual users are participating in these legal changes, and several cottage industries have sprung up around these new policies. And yet all of this is still against federal law, and when federal law is applied, it is often the common people in the middle who are hurt. Below is a good article about this conflict between state and federal law that discusses in very specific terms what you need to know. In the meantime, something has to change. This contradiction between state and federal law has created an untenable situation that cannot endure.
NOTE: More recently, Congress passed a budget that contained an amendment prohibiting the Department of Justice and the DEA from using their funds to interefere with state laws that permit medical marijuana. This is a step in the right direction, but realize that this amendment is only in effect for about a year, the lifespan of the current budget legislation.