I posted this in the comments of the most recent Bitcoins and Gravy episode that included the Peertracks interview, but I think it deserves it's own post...
After listening to the interview, I decided to go over to the Bitshares Talk forum to try and better understand the implementation of Peertracks and the Bitshares Music DAC.
Prior to doing this research, my basic understanding was that the BitUSD used on Peertracks was the same as the BitUSD used in BitsharesX. This is not the case. Each chain (Bitshares Music and BitsharesX) has it's own internal market to establish a USD asset peg.
There is currently a plan being discussed on the forums to merge all Bitshares DACs (BitsharesX, Vote, DNS) into one SuperDAC so that BitUSD is fungible between all of them, but according to Cedric, Bitshares Music will continue to operate as a separate chain.
Peertracks BitUSD != BitsharesX BitUSD
Even though both are pegged to USD, there will be a separate market rate for each which could cause significant slippage if trying to move BitUSD between chains.