Today, I learned that Portland, Oregon has no sales tax. None. Zip. Nada. This means that it is always worth the gas to drive to Portland for shopping sprees, major electronics purchases, buying furniture, and even liquor runs.
If I were to purchase $1000 worth of stuff in Seattle, $30 would go to the city, and another $65 would go to the state. I typically spend about $45 on a tank of gas to drive to and from Portland (from Roy Street Coffee on Capitol Hill in Seattle.) Even if I consider that a round trip to Portland for a shopping spree is at least 350 miles of driving, and even if I use the government mileage rate of $0.235 per mile (the $0.56 is only for business purposes, not general travel) then I would only need to spend about $866 to save the $82.25 that I would spend on gas and wear & tear on the car. Of course, if I took the $30-$40 bolt bus, it would pay off even more quickly!
Woot!
Of course, the state of Washington spoils the fun by insisting that anything purchased in this sort of a situation is covered by a "use tax." Here is a link describing everything that you need to know (and ignore):
http://dor.wa.gov/content/getaformorpublication/publicationbysubject/taxtopics/usetax.aspx
But, Oregon does not report any of these purchases to Washington, so they have no way of knowing, so have fun with your shopping sprees in Portland!