Nothing, really. Except that it would be a taxation nightmare, since every time you spend some you need to report the difference in price between when you acqui

Nothing, really. Except that it would be a taxation nightmare, since every time you spend some you need to report the difference in price between when you acquired it and when you spent it, and pay tax on the gain/loss. It would also be a lot of effort to find people willing to accept bitcoin for things like groceries.