There is risk, and there is just suicide.

What do you believe is the probability that a 2 TH/s miner that costs 7.5 BTC today and will be delivered at the end of April will ever mine 7.5 BTC? That it will ever mine 15 BTC?

Give numbers for probabilities on different amounts of return, we'll turn it into a bet, put funds in escrow, and you can buy lots of risk from me assuming that my probablities for positive returns are much lower than yours (which they'd have to be if you think buying these devices at current prices and pre-order lengths is wise).

My argument against the current prices has nothing to do with risk aversion. I will happily take on a risky investment (including bets over future hashrate with you, assuming the funds are blockchain-escrowed), it's a question of the distribution of risk vs profit. I can go to the stock market and get expected returns of 10% for a particular level of risk and use margin to multiply that up if its not risky enough or dillute with bonds... but there is a risk reward trade-off, and right now I think that the payoff matrix for a lot of mining products looks more like the payoff matrix for the intravenous administration of drain cleaner than a rational investment.

But hey, if you like crazy bets, I'm game to take you money.  There is no need to give up your funds to hardware companies and waste your time, noise tolerance, and power on some mining gear if you're just interested in taking a long shot bet on the future hashrate.