I went to a panel on the problems with the Prime Directive at Chicon 8. There was a lawyer there who actually works with international aid organizations on how they intervene. His biggest problem with the Prime Directive is that it's too simple. They have stacks of rules about how exactly they go about this. There are places where they're not allowed to go because somebody fucked this up bad at some point in the past, and those people don't owe them access just because they promise to be better now.

IIRC, there is a throwaway line somewhere (from Data, I think) that says the Prime Directive is followed up by a hundred little rules defining out the specifics, but it's never treated that way.