Imprecatory Prayer

When, if or ever is it appropriate for Christians to pray imprecatory prayers on people, groups of people, institutions and nations?

Surprisingly, not only are there imprecatory prayers in the Old Testament, most notably in the Psalms of David, but also in the New Testament by the Apostle Paul, Luke and others, such as the martyred Revelation Saints.

Without becoming hateful and using imprecations as a means of personal vengeance or vendetta against our personal enemies, the Bible is clear in both testaments that there are rare circumstances in which calling down God's judgement on the wicked is not only appropriate but needful.