Sorry, but it's not a loophole. In pretty much every state that charges Sales Tax, there's an equivalent Use Tax that applies to goods purchased out of state for use in the state where you reside. The buyer is responsible for paying that tax to their state government. A loophole is a technicality or ambiguity that allows you to avoid the spirit of a law while obeying the letter of that law. Not paying Use Tax on internet purchases is flat out tax evasion. Much like driving 10 mph over the posted speed limit, it's unlikely you'll ever be caught/penalized...but it's still against the law.
I totally agree with you neuro, but where is the line drawn for what must be declared on taxes? Purchased on eBay (new or used)? Craigslist? Garage sale? What is the letter of the law?