Preheat oven to 375º.
Spoon yogurt onto several layers of heavy-duty paper towels; spread to 1/2-inch thickness. Cover with additional paper towels; let stand 5 minutes. Scrape into a large bowl using a rubber spatula.
Melt butter in a skillet over medium-high heat. Add leek; sauté 5 minutes or until tender. Remove from heat, and stir in thyme and salt. Place strained yogurt, goat cheese, and remaining ingredients in a large bowl, and beat with a mixer at medium speed just until smooth. Stir in leek mixture. Spoon pumpkin mixture into a 1-quart baking dish. Bake at 375º for 25 minutes or until dip is bubbly and lightly browned. Serve warm.