so if the price keeps rising, how would we ever use it as a real currency to buy stuff?
i'm pretty sure everybody who has them has them for buy and hold or making profit, not for purchasing goods - I certainly don't because in two months the price might have doubled, and I would curse myself for giving them away "back then" instead of using real currency.
Why buy a laptop? Because if you wait a year it would be a lot more powerful, touchscreen, better camera etc for cheaper. There comes a time when people need to buy stuff almost regardless of future price performance. And of course some people are always thinking we are near the top. And also the price isn't going to keep rising like this forever. It'll flatten out eventually and at that time exchange of BTC we become more common.
But what you've mentioned is the achilles heel of a "sound" currency. It is theorized that during recessions/depressions people tend to hoard it, spending as little as possible -- saving it in case the recession continues. This creates a negative feedback of reduced consumption -> fewer jobs -> more reduced consumption. But on the other hand, in this highly populous, resource limited world careful consumption might be better in the long run than triggering growth that is not connected to greater underlying resource efficiency.