On August 31 Skymal ran a promo offering 25,000 Delta miles for $500 in purchases. That offer has been extended through September 15. (Hat tip to mrp alert in the comments.)
Not all items are eligible for miles, those items and vendors excluded from the offer anre so indicated on the product’s page. And the offer isn’t valid for gift cards. The $500 total spending required excludes tax and shipping.
After browsing through the Skymall site, It’s entirely possible that their products are even more worthless than the SkyPesos themselves!