For business it will be the same as it always has been: You are naturally under the regulation, effective or not, bitcoins or not, of government when you establish oneself as a business. They can use the blockchain to help, but let us not pretend that in itself is a panacea to taxation required for the gears to keep grinding on in the central banking/ governmental taxation systems (which even under loads pre bitcoin, were faltering).

But for individuals, one can create as many wallets as they wish, use as many laundering clients over tor, to remain out of reach. Which is exactly why governments have to set up honey pots to confiscate bitcoins on sites like the silk road (which end up not being effective deterrents and end up being outed as such by the community that relies/favors on reputable past trades). I suspect business/organizations can employ similar technologies to reduce their taxation and how much they declare.