Actually, if you can get a hold of the hardware for it it's anything but a waste since it'll give you more perf/$ and perf/watt. Encoding is one of the best use cases for these kinds of setups. But yeah, it all depends on how serious you are. Wouldn't recommend it for hobbyists. But then again, 4 socket mobo setups would be even worse.

Edit, geek pr0n: