Double or Triple Dip with your Online Shopping. I’ve written before about how you can and should earn miles for your online shopping. All it takes is logging into your favorite store through a mileage-earning site (such as the Northwest Worldperks Mall, the United Mileage Plus Mall, Goldpoints, AirMilesMart, etc. etc.). You can check whether your store gives points, and with which program, at Rewards Lookup.com.

Here’s a tip that’s been a bit of the buzz over at Flyertalk — The Northwest Worldperks Mall gives points for purchasing gift certificates at GiftCertificates.com. You earn 3 Northwest miles per dollar there.

So simply buy a gift certificate for the store you’re about to buy from. The gift cert is e-mailed to you instantly. You’ll get miles for the gift certificate, and then when you shop at the merchant through the WorldPerks Mall (paying with the gift certificate), you’ll earn miles for the purchase too.

Of course, when you pay with your mileage-earning credit card for the gift certificate, you’ll get those miles, too.