This fantasy that Bitcoins will bring governments' to their knees as they find themselves unable to tax people is just that: a fantasy. The following xckd (it keeps appearing in these forums) sums the essence of the flaw in this kind of thinking quite nicely:
http://xkcd.com/538/.
don't overlook how dependent governments are on inflation. there's a good reason they were so keen on abandoning the gold standard.
however, even with a gold standard there were still taxes. but they were so obvious, even a caveman could see them.