it's generally agreed that the NASDAQ was a bubble that burst back in 2000. also housing was in a bubble that burst in 2008.
neither of them went to zero.
Housing drop was something like 40%, though it should have gone lower, and would have, if not for the interference of the Fed. (P.S. it still needs to go lower)
I think a bubble has more to do with mindset than strict numerical definitions.
The subprime real estate boom was irrational, as the market was acting irrational under the direction of the Fed (artificially low interest rates). This irrational behavior, to me, is what makes it a bubble.
Bitcoin could be in one big giant bubble! If we somehow discover this was all a terrible impossible idea, the Bitcoin will crash, and it will have been seen as a "bubble."
However, as the currency gains favor and dependency, I believe we will see more predictable pricing, based on market fundamentals. Bubbles could still arise after this stabilization, but my guess is they would be externally produced - government interference, hacker, or virus to name a few.
Any news that creates hype in the Bitcoin, but is flawed in reality, has the ability to send Bitcoin into a new bubble.
