I've seen some time ago comparison of popularity of passing fads and useful inventions.
Useful invention graph looked like this http://3.bp.blogspot.com/_2IAWpIwOiOc/SuvD_xiOfTI/AAAAAAAAAD... (example was IT) and graph for the passing fad dropped down to almost zero after initial peak (example was Macarena dance, if you remember that you are old ;-) ).
No one here has attended a wedding or bar mitzvah? That silly dance is far from dead, which is not all that important depending on your social set but does give some doubt on the analysis.
Useful invention graph looked like this http://3.bp.blogspot.com/_2IAWpIwOiOc/SuvD_xiOfTI/AAAAAAAAAD... (example was IT) and graph for the passing fad dropped down to almost zero after initial peak (example was Macarena dance, if you remember that you are old ;-) ).
So far bitcoin seems like useful invention.