Preheat oven to 375°. Butter and flour two 8 1/2-by-4 1/2-inch (6-cup) loaf pans (or use Pam with Flour. I think it works best anyhow); set aside. In a large bowl, whisk together flour, baking powder, ginger, and salt. In a medium bowl, whisk together sugars, pumpkin, melted butter, and eggs; add flour mixture, and stir until just combined.
Divide batter between prepared pans. Bake until a toothpick inserted in center of loaves comes out clean, about 50 minutes. Let cool 10 minutes; invert pans and transfer loaves to a wire rack to cool completely. Glaze, if desired.
For the sugar glaze: In a small bowl, mix 1 1/2 cups confectioners' sugar with 2 to 3 tablespoons water until mixture is smooth but thick. Place waxed paper under rack for a quick cleanup. For easy pouring, transfer glaze to a liquid-measuring cup, and drizzle over loaves. Let dry 15 minutes before serving. Makes enough for 2 loaves.