This:
There is no nominal value, they start out valued just like bitcoins did.
And this:
So, by this simple analogy, I hope I have shown that the BitShares system is really no different than existing banks except that instead of issuing new USD with your house as collateral, it issues new USD with the bank stock as collateral.
So, there is a big difference and this simple analogy is not quite useful.
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Aside from price oscillations around parity there is only one way to keep the value of BitUSD equal to FedUSD. To issue 1 BitUSD if you get 1 FedUSD and to pay out 1 FedUSD when 1 BitUSD is redeemed. FedUSD units are not part of any block chain for they are property of Federal Reserve. Where FedUSD units reside?
BitUSD is a prediction market on the consensus value of BitShares vs FedUSD and that is all it is. Consensus value will track the value of FedUSD without ever having to store FedUSD with any trusted party. Anyone who doesn't invest according to where the consensus is going to move will lose money.
As far as no 'nominal value', when we started Invictus Innovations the 'nominal value' of the stock was meaningless until someone decided to give us real FedUSD in exchange for said stock. We could easily issue an IOU USD to one of our shareholders in exchange for holding some of their shares as collateral. In this case what we would be doing is converting a personal IOU USD from the shareholder into an IOU from the corporation that is backed by equity. The IOU from the corporation is much more valuable than an individuals IOU, especially if the IOU is backed by equity.