Sell into what? Both dotcom shares and USD are promise-papers. Bitcoin is the only money in the entire world that you can truly own. Even gold you can't own completely. At some amount you have to put it in vault and hire people to guard it. But you can put millions of Bitcoins in your brainwallet.
The price of anything, especially Bitcoins, is driven by demand, greed, speculation, and irrational market behaviors. It's people running the price up, not math and science, but people. At this moment those people will be become either winners or suckers. The suckers will be the ones who believed the math of Bitcoin makes it magically valuable just as those who believed that Pets.com had a bright future.
I elaborated on this recently: http://blog.oleganza.com/post/67362431718/you-can-own-bitcoi...