Bitcoin's bubble and implosion is fairly sad to the geek in me because they are conceptually very clever. They recreated cash online which doesn't sound like much until you try and think of your own solution to that which doesn't rely on a third party to hold an account owned by each of them and move deposited funds from one to the other. Instead a token of nominal value mutually agreed upon by the two parties can be exchanged directly from the one to the other without involving any outside authority, with no oversight, securely. It's a really clever solution to a very difficult problem.
The degree to which we needed cash online in the increasingly cashless economy is questionable and the huge fluctuations in value caused by speculation have rendered it useless as a means of exchange but it's still a cool solution to an interesting problem. I always get frustrated when people, particularly older people, view something like gold, which is priced far above its industrial uses would suggest, as a rational token for exchange and yet panic at the idea that the US government isn't backing up the value of bitcoin. The value of gold is an ongoing greater fool theory, people are happy to buy gold at a price far above the utility they expect to get from it because they are confident that if they had to they could find someone at least as stupid as themselves to take the gold off their hands for an equal or higher price. The difference between bitcoin and gold, if we ignore the marginal industrial utility of gold which bears very little relation to the price at which it is exchanged, is that bitcoin has a smaller supply of fools.