Bitcoins are like bitcoins. 

My legal understanding of Bitcoins is that they are a form of Prepaid Access without an Issuer.  Like a decentralized Visa Prepaid Debit card. (Terms have changed recently, a few years ago, this would be referred to as "Open Loop Stored-Value").

http://en.wikipedia.org/wiki/Stored-value_card

* I am not your lawyer or accountant, and the legal definition of bitcoins are still not clear.

They are SR tokens 

Legally, bitcoins are not mentioned in any legislation, so the first judge will need to decide. They could be pieces of information, monopoly money gone wild, commodity, voucher codes, money, whatever. But anyway their perceived value should be recognized e.g. in a case handling hacking or theft. By design they are electronic commodity money.

It could also be regarded differently according to the purpose for which its being used and who's assessing that use.  How it's regarded in terms of taxation may be totally different to how it's regarded for AML compliance.

Bitcoins are a mechanism for storing a mixture of reasonable hope and outrageous delusion.
The basic unit might better have been termed the 'speculaton' than the satoshi.

It's arguable that shares and bonds are similar stores of speculative value - but Bitcoin is purer in that regard.

I'm assuming you meant this in terms of taxation and it would be neither, but it would still be considered a capital gain. Think of it as a stock transaction that you would normally file in schedule D, e.g., you bought 100 shares at $1, sold 100 shares are $2, you pay (short less than a year, long more than a year) capital gain of $100. Whether someone will get smart and actually see these transactions, I wouldn't know, but I've been curious myself. Any bankers know what would happen if I were to transfer through ACH $40k from Dwolla to Bank of America? Would there be any paperwork or flags? I know there would be if I went into any bank in the US and deposited over $10k in cash.