Official link: http://pages.ebay.com/promo/decholidaylist/

From December 27 through December 29, 2011 (the "Promotion Period"), sellers will pay no Insertion Fees per item listed ("Promotion") for up to 50,000 listings in the Auction-style format. The Buy It Now option may also be added to these listings for free.

This Promotion applies to both eBay Stores subscribers, and sellers who do not have an eBay Stores subscription. If you do not have an eBay Stores subscription, your listings, up to 50,000 total during the Promotion Period, will be in addition to the 50 free Auction-style listings with free Buy It Now that you already get.
I've listed some computer-related items, one of which was not worth the time for the very small $ return before today.