To simplify my explanation as I really need an answer to this: If I put up a listing with a specific Bitcoin value which is pegged to a value on http://bitcoinexchangerate.org it will be true in that instant (obviously). However if the value of Bitcoin goes up or down even slightly the value becomes invalid when Silk Road updates its price as Silk Road does not currently synch to the same data used by bitcoinexchangerate. The site bitcoinexchangerate uses the same information as MtGoxLive, and MtGoxLive supposedly has the most accurate information according to Silk Road: http://dkn255hz262ypmii.onion/wiki/index.php?title=Seller%27s_Guide#Escrow_HedgingQuoteIf you need the most up-to-date USD/BTC exchange rate, we recommend mtgoxlive.comI could see why no one has bothered with this question before as the synch is somewhat accurate, but all vendors currently stating they have pegged a product to a specific price are technically currently lying unless they've used some other site which has a perfect synch I'm not aware of yet.Edit 2013-06-15: By chance I found a post by Libertas which explains the system a bit more in detail: http://dkn255hz262ypmii.onion/index.php?topic=171221.msg1225291#msg1225291 - however this also makes it clear it's very hard to find the exact value without access to a site which translates exactly those values at any given time.