What are some of the ramifications in the legalization of pot on a state level?

If you live in Colorado or Washington and purchase marijuana from some legal and regulated source and if included in the price of the pot were state taxes that are destined to be utilized to finance some function or program of the state what are going to be the ramifications if you are arrested immediately thereafter by a federal agent on federal drug laws? Is the complicity of the state going to complicate the prosecution of the federal laws? Will you be able to claim that since the state receives revenue from your purchase it is therefore a legitimate purchase? Will the federal government be forced to prosecute the state as an accomplice in a drug transaction and if so, who within the state government will be required to pay the price? The Governor? The Attorney General? The Tax Assessor/Collector?