The flavor of a curry usually improves overnight. Harsh overtones mellow and disparate elements combine for a richer, more coherent result. Some people think this is just because the flavors from whole spices have more time to infuse (and larger chunks of vegetables and meat exchange flavors with the sauce base).
However, I think there's more to it than that. Even with a curry without large chunks of food or whole spices, the flavor still seems to improve over time. Is this really so, and if so, why?