I like the idea of anonymity of a virtual currency in principle, for it's own sake and not for tax avoidance or as a conduit of unlawful activity.

There are no sales taxes, VAT taxes or income taxes paid on any virtual "currency" sale paid unless voluntarily declared by taxpayers. This I can see as a threat to governments worldwide. So virtual currencies will become, should they continue legally, subject to ever increasing government reporting and/or licensing.

A pork belly futures trader would go ape-shit over a Bitcoin futures option on the COMEX -- the volatility would be a money maker