If I understand this metric correctly, it gives us some measure of how much design/development team optimized the performance onto the given die size.
I see the best use of it when comparing ASIC technology chips, since they are 'application specific' chips for bitcoin mining (GPU developers had different goals when designing their products).
KnC's chips don't stand well here. They just took some fpga desing, converted it to asic with some manufacturer's standard technique, and are going to put as many cores on a die as they can.
If they did the optimization in a range as Bitfury, Avalon or BFL, they would have a chip capable of 3,000 Ghash.