Imprecatory Psalms

I don't understand how we pray that the Lord smash our enemies when we know our own sin and that we were enemies of God but that He has been gracious to us. If we are the recipients of mercy, and if God's mercy has captured our hearts, and if God wants all to be saved and to come to the knowledge of the truth, wouldn't we desire the salvation of our enemies? Wouldn't we desire that they be turned and become recipients of grace -- they who are as undeserving as we are?

About a year ago, Pastor finally got it through my head that we can pray those psalms of judgment against the true enemies: the devil, the world, the demons, and our own sinful nature.

But when I was praying Psalm 109 yesterday, the psalmist didn't sound like he was talking about demonic forces being judged, but flesh-and-blood people. So I asked about it at the end of Bible class. Pastor didn't have enough time to give much answer, but one thing he said helped a little bit:
We don't pray those psalms out of vengeance nor out of a desire to get even or to "stick it to them." We pray them because God's law is true. We pray that God's judgment be meted out upon His enemies for the honor of God, not for satisfying our own sinful desire to hurt those who have hurt us.

Gotta think on that some more...