Sounds like a defect in the technology to me. A good currency should be able to support the full range of social policies (like VAT).
One of the problems of the Euro is not being able to inflate different countries within the Eurozone at different rates. If Bitcoin were ever to become popular for regular transactions within many countries, it'd be a fiscal policy disaster. Pretty soon you'd hear Portugal, Italy, Spain, and Greece banning its use, along with similarly wobbly countries in other parts of the world. I remember Malaysia catching flak for halting foreign currency exchange during the Asian Financial Crisis, but it turned out to be a really smart move. It turns out that a globally integrated economy isn't always best for the smaller economies. They need to be able to adjust the spigot.
Edit: I suppose this suggests a feature request for Bitcoin: namespacing, of a sort. If the currency were able to support cross-namespace conversion controls, like a tax determined by a function of the velocity and acceleration of exchange ... that'd be pretty darn cool. Each country could pick its namespace, and have control over its exchange tax function. Taking it further, you could tax intra-namespace transactions. VAT with no bureaucracy. Each account could be tied to a citizen, transactions taxed at some progressive schedule, and then uniformly distributed to every account daily. The transaction tax could be dynamic, to encourage currency flow in bad times, and to add some friction when things are overheating.