Yeah, the idea was that the government couldn't collect taxes anymore due because they couldn't get an accurate idea of what transactions were going on due to cryptography. I figured that it didn't occur to Stephenson that, if you can't crack the crypto one way or another: http://xkcd.com/538/ You could just raise property taxes, because it's hard to encrypt land.

But Stephenson made a reference to exactly that idea in Cryptonomicon, so I don't know what he was thinking.