Preheat oven to 250°F.
Wash the limes thoroughly, and, before juicing, run the limes over a grater (or a zester or micro-plane, if you have one) to get that freshly grated zest.
Squeeze the limes.
Measure the lime juice, zest, salt, sugar, chili powder, and cayenne into a large bowl. Whisk until well blended.
Stir the peanuts into the liquid, and whisk them around until well coated.
Bake for about 30-40 minutes, or until the nuts are dry and just beginning to darken. Remove from oven and let cool.