I'm surprised it hasn't come up until now....at least in a News story kind of way.
I was under the impression that ANY income from sales was taxable. In this article they make a distinction between income from a hobby and from running a business. Not as clear cut as I thought. How long before the IRS audits you over those headers you sold?
The article doesn't address the tax that should be paid by the purchasers as well.
AFAIK if you're not charged sales tax then you're supposed to pay a Use tax.
It's only a matter of time before this huge revenue stream is tapped into by the goverment. Who says the internet isn't like the wild west.
http://story.news.yahoo.com/news?tmpl=story&cid=528&ncid=528&e=2&u=/ap/20050328/ap_on_go_ot/taxes_online_auctions