Isn't the whole idea about currency to be about trust and faith? With money, you have faith of the country backing it up. This of course doesn't mean much for Venezuela, but it means plenty for US, Japan, EU, Canada, etc. When it comes to gold, we all know how hard it is to mine it, so there is also this faith that it will be worth something.
When it comes to bitcoin, where is the faith? Sure you can use it now, but just as quickly as My Space went down in flames, bitcoin can also move onto the next one as has been pointed out. There might be a built in limit to how many you can mine, but who will back it? What is behind it? Its only backed by the hope that someone else will give you something for it.
This idea of backing works well for a country. Its after all the reason why a country can issue treasuries but not individuals. Individuals die, but countries generally don't, so you have faith that the paper currency is backed by something, even if its diluting away. All those citizens in that country represent a united front. Its why they don't allow competing money in one country. If you let a few different currencies in one country, it automatically dilutes the faith in any one.
Even when it comes to land, you have faith that tomorrow, it won't be a toxic waste dump, or covered by volcanic lava flow. You can be sure the land will be worth something, that someone will give you something for it, that your political climate will recognize that you own it and can do something with it. If you didn't have any of this, the land wouldn't be worth anything since someone could just take it away.
So with bitcoin, there is no faith that tomorrow it will be worth anything. We might wake up to the next greatest thing and when you wonder who's got your back, there is nobody because nothing is backing it up.