This was a response to Detroit Dan in comments here, but since the comment is about an Yves Smith post that I have to linked to here and here, I'm posting my reply here for those who may also be wondering about the recent Fed accounting change. The Yves Smith post is a discussion of how the Fed plans to handle any interest rate/market loss it could incur if it decides to sell the hoard of Treasuries it bought via QE2.
Basically, if the selling results in a net loss to the Fed, it will just consider the current loss to be deductible from the amount of profit it sends to the Treasury the next time it has a profitable year. So during the year that it incurs the loss, it actually receives a "credit" from Treasury.
A comparable scenario in private business is if you have a business that incurs a loss this year, you just say "it's okay,I will in the meantime just consider the loss as a shareholder loan from me payable to me the next time the business is able to". This can go on indefinitely if you are like the Treasury, which can just debit-credit the losses until the Fed finally is able to pay again. But you, as a currency user, will have to fund the loss with actual money, while the Treasury, a currency issuer, doesn't.