Damn. Sometimes I can't believe it. I have been following bitcoin quite closely for over 18 months now. The ecosystem is growing in ways only a few bold people have predicted. Fundamentally, it is about belief and trust. The protocol has largely proven itself. People are starting to believe in bitcoin. This is why the price is going up.
For those who say "It isn't being used as a currency!" here is my response:
Bitcoin excels as a secure protocol for tracking account balances in a decentralized, seemingly untamperable fashion, as well as transferring value very quickly to anywhere in the world at the sole, uncensorable discretion of the owner. It is both a payment protocol and a distributed ledger. A lot of people want these unique feautures, even if they can't buy groceries with it yet. Those types of merchants will always be the last to adopt.
Bitcoin also has the pontential to be used in diverse ways as "progammable money". It has a built-in API, and features like timelock, mutli-entity transaction signing (built-in escrow), and others that I don't fully understand. An AI bot could utilize bitcoin (might have trouble with a bank account!).
Also, see gold and its $8 trillion of largely made-up valuation (not stemming from industrial/ornamental demand). You don't see gold owners buying things with a few shavings ;) Bitcoin is far superior to gold in almost every way (it isn't quite as shiny tho). If society can make up several trillion dollars of monetary valuation for gold, then I definitely can picture bitcoin snagging a pretty decent slice (right now it is only 1/3,000 the size gold).
People recognize this potential, and thus choose to invest. The first mover advantange is massive. Network effects are very important - it will take quite the innovation to unseat bitcoin, and it has to be something that can't be simply copied/integrated into the existing protocol. The whole thing is sort of a self-fullfilling positive feedback loop. I'm a cautiously strong proponent, and find it absolutely fascinating to watch. These kind of events don't unfold that often.
TL;DR - magic internet money!
Sorry for the multiple edits. I wrote this on my phone.