Granted the question is GPU vs. Eruptor USB, but has anyone considered how fpga(s) stack against the Eruptor USB.  I'm actually using fpga(s) because:

1) They're similar to the Eruptor USB at ~ $1 per MH
2) They use more electricity than the Eruptor USB, but not that much compared to GPUs  (my Lancelots use 28W compared with GPUs at 100W)
3) And this is the key point for me... fpga(s) can be repurposed (assuming you know how to edit bitstreams) and have more resale value compared to the Eruptor USB.

Unless the Eruptor USB comes down more in price... it's not worth it from my viewpoint because it has no resale value and the amount of time to recover costs is not significantly better than fpga(s).

Anyhow my 2 bitcents...