Stuart, I think you’re wrong that big purpose-built farms will be undercut by regular users because they already have a system anyway. Specialized builds can be made far more efficient in power usage. It’s not a bad thing at all though, it will mean a dirt cheap, safe and private cloud system.
As for your comparison to the dollar being backed by gold, I think it’s off the mark. Gold is scarce, computing power is not. Hence it made sense to be able to exchange a dollar for a fixed amount of gold. The dollar was simply an IOU for gold. Computing power cost decreases exponentially and it’s supply increase exponentially, and thus a fixed exchange rate baked in the network would mean the value of SafeCoin would decrease exponentially and would exponentially inflate. P.O.R. as explained in the whitepaper is backed by computing resources directly, it’s even denominated in computer units of measurement.
I agree that the market itself has to figure out how much P.O.R. you can buy with SafeCoin. I don’t see an alternative to the supply/demand system, it’s the best way to discover the price of SafeCoin. SafeCoin can get it’s special status by being uniquely treated by the MaidSafe network.