To prepare the vinaigrette, combine blueberries, shallot, vinegar, sugar, and salt in blender or food processor and process until blended. Add olive oil gradually and process until smooth.
To prepare the salad, trim tough stems from spinach. Place one radicchio leaf on each of 8 plates. Top with 1 cup of spinach and sprinkling of blueberries, pecans and feta cheese. Drizzle with vinaigrette.