Bitcoin is not like the subprime bubble. It is more akin to a third world currency that has high volatility.

The problem with the subprime mortgage crisis is that the structure of repackaging large lots of mortgages into complex derivatives had little underlying value because the increase in issuing risky mortgages inherently meant they had less value than suggested. Simple math would have shown that many of the loans would be defaulted on, and the value would evaporate. It was a disaster all the way up.

Bitcoin however, derives value directly from the market being backed by a monetary value, and supply and demand. Yes we have seen steady decline from our $1200 peak, but the type of implosion of subprime was in a matter of weeks or months and completely destroyed companies as the value evaporated.

The question is not whether Bitcoin is a bubble or not, it is how do we derive Bitcoin's value and is that justifiable. Currently it is more a speculative insturment like small currencies, or commodities, so it's completely in the hands of traders. In order for Bitcoin to avoid volatility it will need to increase market cap so that 1 million dollar orders can't dump the market. Until then it's easily manipulated.

However, look at the Euro it's seem a major decrease in value because of QE and it's a major world currency, does this mean the Euro is a bubble or the inflationary economic models of existing systems are riddled with problems. The one thing Bitcoin does have as an advantage over other currencies, is it's like gold it can only be found so fast, and there is only so much of it.