With bitcoin you can easily conceal the source and just run a fake hosting company or phony software dev site and cash as much drug money as you want. No way to prove you didn't sell software, plus with NDA's and corporate rights you play the system at their own game.
It's still a drop in the ocean of laundering compared to the millions in cash that cross the US border into Mexico every single day hidden in semi trucks. Here's a good pdf outlining the techniques cartels use to distract border guards with decoys while their trucks full of illegal shit sails straight through
http://www.all-about-psychology.com/support-files/drug_smuggling_part_2.pdf after reading that you'll realize what a wasted effort the entire war on drugs/laundering is. It's actually laughable to think they would go after Bitcoin for laundering when there's rows of corrupt banks washing billions for the cartels just across the border.
Just watched
How To Make Money Selling Drugs, great movie by the way, and they explained, again, why the US War on Drugs is just bad, racist and cruel policy, and former prime-minister of my country appeared in the movie, he was one of the main politicians here who pushed the drug consumption decriminalization, I was also part of the liberalization movement 13 years ago.
And I've seen my country being used as a good example for this kind of policies in several US documentaries, I grew up in the pre-decriminalization and 13 years after things are much better, it has been done, it works!
On the topic, for money laundering you just have to know someone at Vatican, top notch money laundering folks, like "Monsignor 500", he got that nickname because his wallet was always packed with 500 Euro bills.
http://www.ibtimes.co.uk/articles/484346/20130628/vatican-bank-nunzio-scarano-monsignor-500-switzerland.htm 
