I agree with Doug that e-commerce is ripe for the plucking and sales tax is the low hanging fruit. The process of legislating the situations in which the tax is collected, and who collects from whom, is going to be like wrestling an alligator. I recently learned about the Streamlined Sales Tax Project, which, according to Wikipedia, “arose in response to efforts by Congress to permanently prohibit states from collecting sales taxes on online commerce.” Here’s a worthwhile intro to the SSTP: http://www.nolo.com/legal-encyclopedia/sales-tax-internet-29919.html

Based on the growing size of online sales, poor fiscal condition of state, local, and federal / national governments, and legislative climate, it’s clear that e-commerce is a juicy target for tax authorities and it’s not going to make sense for most online merchants to do deal with these issues on their own.