It differs from state to state, and even then each states dictates conditions and rules. For instance in Massachusetts when that had it 2 years ago (they didn't offer it last year) They capped the cost at 2,500 so some of the Macs apple sells would not have qualified.
By the same token we "Mass-Holes" as some new hamphire folks call us Just drive to New Hampshire to buy our computers since they have no sales tax
Tax free weekend starts on the 6th in NC. I can't wait! That's when I'll be ordering my MBP. It's sad really. I've been saving for months and I remember thinking... well I could wait for tax free weekend, but god is that far away. Now it's less than two weeks.
The tax free weekends are targeted at back to school shoppers. A lot of the people that wait for them wait to get them because they qualify for the EDU discount. In the end, some will get:
EDU Pricing -$50-$150
"Free" iPod touch
That's not something Amazon can do.
Finally, unless you live in a state that doesn't have sales tax, the purchaser is required to pay the tax after the fact. Few do and only a couple retailers like Apple charge the customers - but, just so no one leaves with the wrong idea: you legally are required to pay tax.
"But Mommy, they said there was no tax on teh internets"