"It will be different this time" is often heard just before a sovereign debt crisis, stock market crash, real estate crash, etc.  It is the best indication that a bubble is happening.

The question is how much value of bitcoins is in their utility as a currency in real transactions, and how much is in speculation on being able to obtain dollars for them in the future.

Once the value of speculation is higher than the utility of bitcoin as a transacting currency, the bubble will no doubt burst.  In the Netherlands, at the peak of tulip mania in February 1637, prices rose 1000%.  By the next year, tulip prices dropped to their pre-bubble price.

Add South Sea Company bubble, Mississippi Company bubble, Dot-Com bubble, etc.

The Great Depression is another very interesting example - stocks were likely overpriced by bubble phenomenon, but what popped the bubble was deflationary pressure by the Fed.  Which is pretty much the situation bitcoin is in.

If bitcoin's money supply provided a stable value currency (neither inflationary nor deflationary), I think it would grow into something in the long term.  Given the current algorithm, I give it under 3 months.  After the bubble burst, I think interest in bitcoin will fade away.

A great social economic experiment though!  Someone's Ph.D. will be made examining the upcoming bitcoin bubble burst.