Just thought I'd fend this off before Illinoisans go crazy over this law talked about in this article:
http://www.wqad.com/news/wqad-state-wan ... 6927.storyI've had a lot of experience dealing with this as an e-commerce website programmer (my primary job from 2000 to 2009). I'm not a lawyer but have had a lot of experience. Websites must collect sales tax for the state in which they do business (i.e. have a brick-and-mortar store). The sales tax is calculated on shipping address, if I recall correctly. Most reputable websites do this properly (i.e. Walmart.com, ToysRUs.com, Target.com, etc) and the ones that don't you probably don't want to buy from anyways. I'm sure the state is far more concerned about going after retailers who don't collect sales tax than the individual tax payers who somehow didn't pay tax on a website that should collect tax.
If you buy something online from an Australian retailer, you don't have to pay sales tax.
If you buy something from Amazon.com, I don't believe you have to pay sales tax because they don't have a brick-and-mortar store in Illinois unless you buy something from a seller in Illinois, but even then I'm pretty sure they have to have a brick-and-mortar store here in Illinois (though I wouldn't be surprised if that part of the law changed to just being located in Illinois).
Other examples ...
Wisconsin Transformers fans have to pay sales tax on BigBadToyStore.com.
Illinois Transformers fans should pay sales tax on Toynk.com
While it might apply to some eBay purchases, I think most of our purchases as collectors are most likely fine as they are. I wouldn't get your panties in a bind over this.