As delightful as the runup in Bitcoin's price is, I am much more fascinated by the ability to sign contracts with Bitcoin keys. Granted, this has always been possible with PGP/GPG, but blockchain and distributed payment feature make bitcoin-qt the basis of an entire financial system.
That is a good thing - but we all have our 'AH-HAH!' moments.
For me - with what might be considered an unusual life-history - the moment was understanding that bitcoin is absolutely unstoppable by national borders. I saw that instantly, in my first exposure to it in Q1 2011. I had miners up and running within the week.
It may not be particularly anonymous, or (given a certain lack of stability at the moment) usable as a pure currency - and overcoming these and other obstacles will probably result in the promise of low fees being put off for awhile; if not forever.
But that one thing: transfer across borders without any possibility of interdiction... that's really all that's needed for a major change in the way the world works.