Every time someone buys a product with their bitcoins, they now have to declare profit or loss for that transaction compared to value of that coin when they earned/mined it.
This is why I don't think bitcoins have much longer to live. When everyone realizes what a nightmare that is, why would you possibly want to use bitcoin instead of cash? I'm going to continue mining because I'm getting free electricity...but I started mining initially because I BELIEVED that bitcoin could make a difference and be something special, and I wanted to be a part of that. This tax code kills it for the average consumer.