[ufmace]

There was a good post on the tax implications of Bitcoin by (what I think was) an actual accountant a while back. The gist is that it's taxable only when converted to real goods. So if he mined some number of coins early on and is just holding them in wallets, then he owes nothing. Any time anybody sells any coins for cash or any other real goods, they owe tax on the difference between the sale price and the original purchase price.

There hasn't been much formal on "purchase price" of mined coins as far as I know/remember. It's probably safest to treat them as a purchase price of zero, thus if you sell mined coins for $100, then you have a $100 income that you owe tax on. A clever accountant might be able to claim that mining hardware, electricity, etc, is the cost of acquisition, and so offset the sale price in that way, but it probably isn't worth the trouble for Satoshi or anyone else mining in the early days.

[PaulAJ]

As I understand it, if you are doing mining as a business then you treat your mining hardware, electricity costs etc as business costs to be subtracted from your income when figuring your profit. If you buy some BTC at $100 and sell at $150 your profit is $50, as you would expect. Similarly if it costs you $100 to mine bitcoins that you then sell at $150 your profit is also $50.