The value of BTC has risen a lot in the few days I've been here. I notice lots of prices that are high now because people aren't used to adjusting downward quickly. Obviously the increase in value will slow down, but in a longish auction you might end up getting bids in the beginning and then no more because the BTC are more deal at the end of the auction than they were at the beginning. I'm not really saying much here, just that I'd expect people to prefer short auction lengths. Of course not too short because you want enough people to see it before it goes offline.
The prices could be listed in National currencies and then the payment accepted via bitcoins at the current market rate. This way some one could immediately turn them back into the cash they are used to using until BTC becomes more widely accepted.
I don't think this is so good because there is no one market rate. There are and will be multiple exchange markets that have different 'last' trades due to different closing times, down times, random large orders to buy or sell pushing prices temporarily apart. Arbitrage seekers will move them together over time, but while the markets are so thin you can have moves of 20% in minutes.
I think it's best to quote a price, but note that it's subject to change.
Maybe when buyers make offers in terms of BTC they should give an expiry time or date at which they are no longer committed to buying at that price.