This week, Google made some major changes to their search engine algorithm, calling the update "Panda 4.0." As a result, many websites were booted from high-ranking search results, but none has suffered as much as eBay. Pando 4.0 has stripped an estimated 80 percent of eBay's best search results. 

It's unclear exactly what motivation Google had here, if any. EBay is a major money maker for Google, and the two have had a generally positive and mutually beneficial ad sales relationship for some time now. eBay is the second largest customer of Google's product listing ads (paid shopping, known more commonly as PLAs.) They spend hundreds of millions on these ads. 

via Business Insider.

Larry Kim, CEO of Wordstream, a search marketing company, told Business Insider that eBay's fall from SEO grace is partially their own fault. "eBay's asleep-at-the-switch AdWords management style not only made them look stupid to searchers – those irrelevant ads also cost a brand a ton of money. Their failure to implement even the most basic of paid search best practices, like using negative keywords so you're not appearing in queries for vomit, made their research completely unreliable."

As for how poorly eBay fared,  over at The Moz Blog put together this chart:

via The Moz Blog

Other major SEO losers were ask.com, Biography.com and RetailMeNot.