If Bitcoin is not a currency then what is it?

* It has a current set value against other currencies/cryptocoins
* It has value
* You can buy goods with it/sell it for other currencies
* It is obtained by working (mining)
* Any other currency type quality to be added here...

Regarding the tax situation - at some point this will be implemented by governments if they can work out how to track the transactions and identify back to the owner.