In california, it has been mixed. The fact is that there really aren't many federal officers, so a federal indictment for drug possession is fairly rare unless you're a major dealer or doing something stupid like lighting up at an airport.
On the other hand, the feds arrested a person growing marijuana FOR the city of oakland in a very public way. You can read all about the plight of ed rosenthal here:
http://news.google.com/news?hl=en&lr...al&sa=N&tab=wn
Here in CA, we have prop 215, which mandates treatment for minor drug offenses rather than prison, but that only goes to the state and local level. At the fed level, they can still do what they want.