An October 2012 survey of the top one million sites (in Alexa) puts into perspective just how popular Magento, the ecommerce platform within Ebay's X.Commerce platform), has become. 

Magento captured 23% of the market according to research conducted by Tom Robert Shaw, a UK Magento developer at Meanbee. That equates to just over 8,000 sites of the top one million (Magento also lead in the top 100,000 sites). Magento has seen growth in every edition of the that particular survey since it began 2 years ago, experiencing a 20 percent growth rate since the last survey in February 2012. 

Ecommerce platform ZenCart also seemed to fare pretty well, capturing 12 percent of the market. Both Magento and ZenCart both released new versions since the previous survey. Also noteworthy were that VirtueMart and OSCommerce experienced a dip in market share, while PrestaShop and OpenCart saw significant increases.