Well, no, he's not really 100% right, as there are quite a few positive aspects to the Killer NIC.
Let me be clear here, no average user has any need whatsoever to spend the money on one of these BUT:
Zenmaster's hypothetical test was completely beside the point. The Killer NIC bypasses the Windows stack, this is where the latency reduction comes from, not from magically changing the speed of bits coming into and out of your modem.
Second, if your system isn't exactly top-of-the-line, you can get a nice little FPS increase. However, if your system isn't tops, you shouldn't spend hundreds on a freakin' NIC either.
Finally, you can do some pretty interesting things with the Killer. It has a USB port that can accept hard drives, runs linux, and can be programmed to perform any number of tasks. While it's not groundbreaking, it is unique.
Again, no reason why anyone REALLY needs one of these things, but it is rather cool and unique. The cost is just too prohibitive. But, if you have already upgraded every concievable component in your system, have a kiddie pool full of hundred dollar bills that you swim naked in, and are familiar with Linux, go for it!