I don't see that it's quite as clear cut as you indicate. For instance, the pool I use has a 0% fee, and so is pretty much an agreement between users to split the value of mined coins equally according to work done. I can't really think of an exact analog in the pre-bitcoin world.
It's all very simple. The value of any property you receive is taxed. It could be labeled as a 'gift' from someone else, or gotten through some other means. Doesn't matter. For example, if you receive 2 btc somehow (and a value that day of $600 per btc), you have received $1200. This $1200 is your earnings for the year. You can then deduct what you have spent (in power, etc.) to get that money. Whatever you end up with, say $700 is taxable.
If you ignore to do this, fine. No problem - unless you're audited, then they'll research your activities and you'll be liable for that amount (or more if they calculate more) plus penalties.
It's always safer to figure it out conservatively, and then if you get an audit, you don't have to worry about anything. In general, in an audit, if the US government feels you knew the law and tried to apply it properly (even if you were off by 10%), they're okay with it. If they feel you tried to cheat them, only then will they try to nail your ass to the wall.