A new report from comScore says that second-quarter e-commerce sales from desktops totaled $49.8 billion in the U.S., a 16% gain. And mobile commerce spending rose by $4.7 billion, or 24%, during the quarter. Top-performing online product categories were apparel and accessories, digital content and subscriptions, and sport and fitness products. E-commerce accounted for 9.6% of consumers' discretionary spending, which it says is the highest second quarter share on record.