I was recently reading this snipbit, http://www.npr.org/templates/story/story.php?storyId=127581050, on how in July BC residents can shop at WA in a tax exempt fashion. Kind of an interesting way to draw out of country shoppers if that was the intent. Although, if you are thinking of crossing the border you still need to keep in mind that you will most likely still need to pay a tax on the way back.
Sometimes with the way things work here you can buy items online for less by purchasing things out of province. Since most local provinces have their own tax usually businesses are only required to charge those particular items for people who actual reside there. So like here we have a 7% sales tax and many times people out of the province who purchase items from here will be able to avoid that tax.
Of course that will change soon as we have a new flat rate tax system coming. So I suppose these types of tax incentives will attract more people to shop south of the border. Interesting timing too considering our new tax system is coming into play soon too.