We've hit a digital milestone: For the first time, consumers are filling up virtual shopping carts more than real ones.

A new survey by the United Parcel Service and the analytics firm comScore found that shoppers made 51 percent of their purchases on the webThe Wall Street Journal reported Wednesday. The fifth-annual survey offers insight into the growing reliance on e-commerce over traditional storefronts, though the trend may not be as straightforward as it appears at first blush.

The increase in online shopping is driven by web giants like Amazon, which accounted for 60 percent of total U.S. online sales growth last year, WSJ reports. A healthy 42 percent of the more than 5,000 survey respondents said they search and shop for their products entirely online--an encouraging sign if you're a small retailer looking to establish a foothold, especially if you sell through larger platforms like Amazon.

The survey results don't necessarily indicate that most bricks-and-mortar stores are going the way of Blockbuster anytime soon, however. This year, for example, 38 percent of customers reported that they compare prices online and in person before buying, underscoring the need for e-retailers to be aware of competing in-store prices, and vice versa.

Finally, the scales may slowly be tipping in favor of digital shopping, but the movement isn't picking up equal speed across all demographics. Millennials, as always, led other age groups in online retail participation, especially when it came to mobile purchases: 63 percent of the young shoppers reported buying goods on their smartphones, while only 9 percent of baby boomers and 8 percent of seniors reported doing so.