For years I have been paying sales tax (VAT) on purchases I make online through services such as Clickbank. It is inconvenient but it is much easier for Clickbank to work this way then to have to monitor the location of a seller and buyer.
The general rules in the US, as far as I can determine is that if you have a business presence in a state, you have to pay tax there. This applies if you own your own servers in the sate, or if you have employees.
Thus it might be beneficial for me, living in Europe to only

When Will New York Introduce A Google Tax?
Today's news is that Overstock have decided that they are axing 3400 affiliates in the New York area because of the previously reported "Amazon Tax" - which Amazon are fighting.
I think Janet was the first to break the news of the Overstock changes
This is a story that both Linda at 5 Star Affiliate Programs and Shawn's Affiliate Blog have been covering in depth.
The New York Times also has coverage and been giving out some great links.
Techcrunch has a Scribd copy of the original Overstock posted letter (Shawn posted the email)
The New York Times reports that