Will an awesome user experience be enough? :) Plus, merchants can reproduce this UX by integrating Paypal, or perhaps Venmo in the future. The user experience is not a fundamental advantage to bitcoin.
"Who would dare purchase anything for 1 BTC when the value of that BTC could go up 10% the next day?"
Early adopters.
With the BTC/USD run-up to $550+, many early adopters who bought bitcoin when it was trading for a few dollars now have very high purchasing power; this will lead to spending, regardless of volatility.
As an example, imagine you purchased 1,000BTC when they were trading at a dollar. Your purchasing power was $1,000 back then. Today, your purchasing power is around $500K. Spending a bitcoin or two on Christmas gifts would make perfect sense to you.
I think bitcoin is only starting to gain wider adoption. There are many indicators that the currency still has a long run up:
* If you look at the numbers, there are today between 400K and 500K people in the world using bitcoin, which is a very small fraction of the population
* A new bitcoin exchange in China, the world's most populous country, has opened and offers traders 0% fees
* India, a country with more than a billion people, still does not have a major bitcoin exchange
* The bitcoin protocol has been around for more than 4 years and has been reviewed by some of the best developers in the world.
Many people are comparing the current run-up to the April bubble. The market today is much more fragmented. There are many, many more players, and thousands of cash-rich investors waiting on the sidelines for a small correction in price action to buy in. This alone would prevent an all-out sell-off.
Others point to how easily it is for one government to shut down bitcoin, by putting pressure on banks to close bitcoin exchange accounts. To do that, they would need a legitimate reason, which they don't have — and this will become more difficult as more legitimate merchants adopt bitcoin, especially the larger ones. If that does happen though, exchanges can relocate their accounts off-shore.
Bitcoin is still very small. The market cap is ~$5B, which is the size of a small company. For a currency that can be used by anyone anywhere in the world, that seems a little... undervalued.
Some of the above price targets may seem crazy, but if you compare that growth to the growth experienced by Apple or Amazon over the past few decades, it starts making sense. And bitcoin isn't a company; it's an international currency, so its growth potential is even higher.