The Court of Arbitration for Sport have ruled that there is no evidence that his prosthetics constitute an unfair advantage over his preferred 400m distance. The initial IAAF testing showed that he used less energy at full speed, but this is not relevant to sprinting performance, which demands maximum power output. All below-knee amputees are at a significant disadvantage during the start and initial acceleration of the race, which is vital in sprinting.
Personally, I think the most obvious evidence that these prosthetics do not constitute an advantage is the times of other athletes using identical limbs. Pistorius is whole seconds faster than his nearest rivals. If the limbs constitute a meaningful advantage, then why is Pistorius so uniquely quick?