"as far as I can tell, mining is currently unprofitable with any reasonable cost of electricity." I have been mining for 3.5 years. This statement is utterly false. Current mining hardware, such as the KnC Jupiter, can mine at about 500 Ghash/s at less than 600 Watt at the wall. Over a month it mines: 500e9 (hash/sec) * 3600 (sec/hour) * 731 (hour/month) / (2^32 * 8.0e9 (current difficulty)) * 25 (btc/block) * 400 ($…
You're completely ignoring the capital cost of buying the miner.
The question wasn't "is it profitable to begin mining Bitcoin?", it was "is it profitable to mine Bitcoin?"
Miners already have the equipment - as long as proceeds don't drop below energy costs, mining will continue at current levels.