Here is the full sermon of Reverend Wright that has received so much criticism of late. The last few lines of it that I have printed below show I think that in context, his "God damn America" is entirely appropriate. Sure the sermon has a lot of politics in it, much of it swallowed wholesale and unreflectively. But the essential reason for which he used this reprise is well merited. He always qualifies the statement in an effective way.
God damn America, that's in the Bible, for killing innocent people. God damn America for treating her citizens as less than human. God damn America as long as she tries to act like she is God and she is supreme. The government of the United States has failed the vast majority of her citizens of African descent.