http://alternet.org/drugreporter/48749/ Some conditions and disorders cause extreme pain where Morphene and Oxyvotten can't help. But Pot can.
I don't think marijuana has ever actually dulled any pain that I've ever had. The most beneficial that I can imagine marijuana being with respect to alleviating pain (chronic or otherwise) is the reconciliation of having to deal with it.
^^^ Actually the anxiety associated with pain is the biggest culprit when it comes to 'feeling' the pain. Basically the pain creates anxiety which creates more pain etc, which creates more anxiety, etc... If you are able to stop the anxiety you can stop the rapid cycle and alleviate the pain. This is why opiates are so damn useful. They've done studies to test the anestetical properties of opiates and found that most barely dull sensation. However, anyone who has done opiates will tell you that they make you just not give a fuck. this apathy is what really helps in pain management. I could see how pot's short term memory issues and tendancy to generate random thoughts could be beneficial here. It's hard to obsess when you can't remember much.