I am gonna help AC out on this one. A link to "the memo" is included below. I also c/p the next to paragraph, which says in essence, go ahead and bust/prosecute anybody you, all preceding paragraphs not withstanding. "The memo" says absolutely nothing although it does take about 500 words to arrive at that destination.
"Finally, nothing herein precludes investigation or prosecution where there is a reasonable basis to believe that compliance with state law is being invoked as a pretext for the production or distribution of marijuana for purposes not authorized by state law.
Nor does this guidance preclude investigation or prosecution, even when there is clear and unambiguous compliance with existing state law, in particular circumstances where investigation or prosecution otherwise serves important federal interests."
http://blogs.justice.gov/main/archives/192