The DEA doesn't report to the president directly in terms of its marching orders--but it does generally respect his wishes to some extent. The DEA is taking it easy for the moment because one of the first things Obama did upon entering office was ask them to stop wasting time raiding dispensaries and worry more about cocaine and heroin being trafficked in.
The DEA under Bush was not so nice, in part because he specifically asked them not to be (he did not respect the Cali law in that time, can't speak to his mind now).
This is one area where rupubs/conservatives are a bit strange--they typically are for states rights and against federal regulation. Not so with the weed. On the other hand us liberals tend to be the guys you might expect to come up with some overly-confounded scheme such as the drug war (hey, we all have our weaknesses). However, in this case is exactly the opposite, for once most of my party thinks bureaucracy is dumb.
Of course you have you dissents on either side--but you can bet if we get a republican in office (worst of all Newt), the DEA will be ramping up its operations again in the kinder states of the union.