How are people still actually using it to _buy_ things?

My problem with this rate of change is that it makes it harder to use it as a means of buying things.

If I see an item for sale for 2.5BTC then it can take me an hour to translate my GBP into BTC. Then I carry out the exchange, and then they have to transfer it back to their currency (if they want to spend it on most things).

If the value has gone up 15% in that time then what price should they be charging me?

Should a shopfront be updating its prices on an hourly basis?

I'm all for BTC being valuable, but it needs to have _some_ stability to be used as a method of value exchange.