J. Robert Schlimgen (J.D. 2011, Minnesota) has published Note, Virtual World, Real Taxes: A Sales and Use Tax Adventure Through Second Life Starring Dwight Schrute, 11 Minn. J. L. Sci. & Tech. 877 (2010). Here is the Conclusion:

Admittedly, states and localities will face many challenges in attempting to collect sales and use tax on virtual goods. Similar problems likely face the federal government as it attempts to impose a federal income tax on the virtual worlds, but the federal government has at least began to explore potential solutions. Unfortunately, states and local governments have once again lagged behind the technological curve. Given the growing budget problems of many state and local governments, it is time for such governments to start looking at options to expand the tax base. Digital consumption is only going to increase in the coming years, and it presents the perfect opportunity for state and local governments to expand their tax base in a fair and equitable manner. Although there may be roadblocks, as shown above, a framework can be constructed to make such a tax enforceable without discouraging a mobile work force.