Check your email because eBay is sending out targeted promotions offering 4X or 5X eBay Bucks for purchases through 2/18/15 at 11:59PM PT. You must click the link in your email to activate the offer.
I personally received a 5X offer, while a number of people in this Slickdeals thread have reported receiving a 4X offer as well.
eBay normally pays back 2% of the purchase amount in the form of eBay Bucks. This means that a 4X offer amounts to an 8% rebate while a 5X offer equals a 10% rebate.
eBay Bucks are earned on all purchases including gift cards. (eBay gift cards are excluded.) See: A new way to increase rewards beyond 5X for more ideas on how to stack your savings.