People seem to love talking about shorting Bitcoin, and a crash wouldn't surprise me all, but given Bitcoin's meteoric rise recently you'd have to be insane to actually do it.
The problem is that there is no supported mechanism for shorting.
If you have a lot faith in bitcoin, will you lend me some at 0% (or negative, if you believe in growth!) annual interest for a 10 year term? If so, I will take that loan.
Even if there were a way, you do not want to short something that jumps 15% in a day even if you believe it's overvalued.
In the long run you might be right, but when you get margin called it won't matter.
Since bitcoins are heavily (completely?) coupled to actually holding them, shorting (which is based on the concept of lending an assert) isn't really possible.
