So what's special about this Killer NIC crap? :/
Well its a NIC with a powerful dedicated processor and its own onboard memory so it can (in theory) take some load off the OS networking stack and things like that.
I remember reading somewhere it was powerful enough to run a firewall on its own which is an interesting idea to releave load on the OS.
In my opinion the performance increase, of which there would probably be some in some minute way, is not justified by the cost of the card itself.