Bitcoin works reasonably well as a medium of exchange, as long as transactions are confirmed relatively quickly.
Bitcoin prices are pretty much always tied to the price in US dollars or some other fiat currency. Online prices can be changed dynamically, so Bitcoin doesn't really need to be its own unit of account.
But it never really works as a store of value, due to its volatility. I have about $20 in Bitcoin today, but I have no idea what that will be worth in a week, so it's risky to keep any large amount of money in Bitcoin. The safest way to buy things in Bitcoin would be to buy it, and then immediately send it to whomever you're buying from.
So I think that Bitcoin will be much more usable when its price stabilizes, and there's much less friction with each purchase.