Here is my overwhelming concern: I don't want to spend $100 one day and find that worth $200 next day. Similarly I don't want to hold $100 and find it valued $50 next day. How would you convince me?
For now I doubt many people have only bitcoins and have at least some cash. For point 1, you can always leave some money on an exchange site and then as soon as you spend bitcoins somewhere, you buy them back on Gox. For point 2, I wouldn't spend my bitcoins until they increased again. For the time being I would say bitcoin is more of a payment system and a store of value, not a currency.