There is only one thing that determines whether the mercurial rise of bitcoin is a bubble, and that is: will bitcoin become a widely accepted form of payment, whose value is no longer measured in $$$?
The answer to this question I do not know, and probably nor do you.
If it does, then bitcoin has value in an of itself. Stories of more and more merchants accepting payments in bitcoin suggests some movement in this direction.
If it does not – if, for example, regulators decide enough is enough, or if there is much more bitcoin hacking – the confidence in it as a store of value erodes, and so does the $ value.
musings of an untrained mind 