I can make virtual credit cards on the spot that require no name, and work anywhere. I can exchange your Bitcoin into a VCC (virtual credit card).
1 BTC [$8.20] = $8.00 in VCC money.
So exchange rate is fluctuating pretty quickly. You might wish to express your rate relative to the latest exchange rate (e.g., that $8 if the Mt. Gox last was $8.20 is about a 2.5% discount, or value of 97.5% of the bitcoin value.)
Does this need to be spent with one merchant, or can I spend part of it with one retailer and the balance at another?
Changed. It can be spent at any retailer, it's a virtual credit card. Just as if you had a credit card in your hand, but you only get the number, expiration date, and CVV.