https://en.bitcoin.it/wiki/FAQ#Won.27t_loss_of_wallets_and_t...
Even without deflation I think there would still be problems with high variance of BTC just from the psychological aspects of the currency. With central banks you can at least say that there are persons whose job it is to watch currency exchange rates and take one or more of many available actions to curb both inflation and deflation. As far as I can see you just don't have that with BTC (and by design). You can't increase the money supply, any action to decrease the money supply is permanent, and how can you change interest rates for loans when all of the money is already issued?
I just can't imagine BTC being useful for transactions in general (especially important stuff like payroll) when the inherent variance in value seems to require systems akin to what a high-frequency trader would use. It might be useful as a commodity for similar reasons that gold is (but with the improvements that come from its high divisibility).
i.e. If BTC gets to be more than $1,000,000 apiece, this will be necessary to perform USD transactions down to the cent. Otherwise, it's not a problem
https://en.bitcoin.it/wiki/FAQ#What_do_I_call_the_various_de...
Well, its different in that pennies are the smallest physical subdivisions of the dollar, but then, bitcoin has no real equivalent (pennies aren't the smallest usable subdivision, there's plenty of places where smaller units are used when dollars are a unit of account but not physically changing hands.)