I have used Bitcoin for purchases in the past. I try not to do it so often because of the exact thing you mentioned, but I feel like this is something that could improve with time.

If Bitcoin does get mass adoption and becomes THE worldwide currency then that also means that the volatility will decrease significantly to the point where I wouldn't have any problem transacting using Bitcoin.

I realize the idea of that actually happening is pretty insane and it is probably more likely that the value will go down to zero, but it is hard to predict the future.