We're displaying prices in dollars for now, but when you check out, you can only use bitcoins to pay.
I like this, though it would be nice to do what I see many websites do- use a drop-down box to select your currency displayed.
Personally I won't shop at any site that doesn't have auto-adjusting prices of some kind (a fixed fiat price with BTC shown later is fine)- at least until the BTC price stables out.