Not entirely a tax amnesty, in that the taxes were forgiven, but that businesses (and it was basically business involved here) could pay up without risk of being legally at risk ... may have helped out Washington in a big way.
How much? When the Washington legislature approved the idea of an amnesty period, the estimate was $24 million. What the state actually got from businesses that hadn't paid up? $321 million - more than 10 times as much.
That's actually been dampening talk of a second special Washington legislative session. Governor Chris Gregoire: "With this information, they can go home."
Maybe some others might try the same thing, and see what they pull in.