I just stumbled over this article:

http://www.forbes.com/sites/janetnovack/2012/03/26/24-states-moving-towards-decision-on-taxing-groupon-livingsocial-deals/

The discussion is, as I see it, also relevant for for bitcoins. Digital currencies like bitcoin are, for a very near analogy to a gift card or a group on voucher. You buy your proof of value and then later you use it in a store that accepts it. The decision by New York and other states to charge tax on the value and not the gift card value is actually accepting a gift card as a for of currency or a proof of depth. I expect bitcoins to be treated similarly resulting in nor sales tax on bitcoins.

We have had a similar discussion in the Nordic/EU forum, but I think the article from forbes indicates that it is a relevant discussion for US too.

Cheers,

Michael