Now another question what if we never change to fiat and use the bitcoins to make purchases lets say for non-business related expenses?
Hey! Look over there! *quickly runs the other way*
heh. I'm not a lawyer or a tax accountant. What you are asking is uncharted territory. Gov.s aren't stupid. They are going to demand their piece of the action one way or another. Once enough people start using Bitcoins in their daily transactions the Gov. will notice and demand their taxes. It will probably take some time though. Perhaps the day will come when the Gov. will accept the taxes on the bitcoin portion of your income in bitcoins. Most likely though, they will factor in some average exchange rate like they do for capital gains made on multiple stock purchases all liquidated at once.