I was listening to Ian Hamilton this morning on the way into work speaking on Psalm 28. When he came to vss. 3&4 he gave an excellent explanation for the statement by the Psalmist, Do not drag me off with the wicked, with the workers of evil, who speak peace with their neighbors while evil is in their hearts. Give to them according to their work and according to the evil of their deeds; give to them according to the work of their hands; render them their due reward. Rather than explain away that under the New Covenant the concept of forgiveness has changed somehow, he directed the listener to Luke 18:7 which states, And will not God give justice to his elect, who cry to him day and night? Will he delay long over them? In other words, the Psalmist is just asking the Lord to do what he says He will do in Deuteronomy, that is, bless those who are obedient and curse those who are not. Luke 18:7 simply confirms that nothing has changed under the New Covenant.
The imprecatory Psalms so often confound modern commentators. They are, and sometimes very creatively, explained away. Others ignore them and others choose not to believe they are canonical. The above is one of the simplest and most direct explanations I have heard. Many thanks to Ian Hamilton for making what others think so difficult and easy concept to understand.