The widely cited Boston Consulting Group’s annual digital economy impact report is out and it once again makes for reading that should make any entrepreneur, marketer or politician take notice. The big number is $4.2 trillion. That’s the amount the Internet economy will contribute to the G-20’s total GDP as of 2016.

David Dean, BCG senior partner and a coauthor of the report, says “if [the digital economy] were a national economy, it would rank in the world’s top five, behind only the U.S., China, India, and Japan, and ahead of Germany.” And, the Internet economy is expected to grow by more than 10 percent a year through 2016, according to the new report.

We’ve already seen the impact of digital in other business sectors. As we reported earlier this month, the global ad market growth is expected to outpace global GDP growth thanks to a host of factors, the rise of digital advertising being one principle one.

Here’s what caught our eye:

• In the developed markets of the G-20, the Internet economy will grow approximately 8 percent annually
• in the developing markets, it will grow at an average annual rate of 18 percent
• Argentina and India will grow the fastest, at 24 percent and 23 percent a year, respectively.
• The leading developed markets—Italy and the U.K.—will grow about 12 percent and 11 percent a year, respectively.
• In 2010, the Internet economy in the U.K. accounted for the highest percentage of national GDP (8.3 percent), followed by South Korea (7.3 percent) and China (5.5 percent). In each of these three countries, the Internet economy would rank among the top six industry sectors.
• In the UK, the digital economy will be bigger than healthcare, education and construction as of 2016.

One of the most interesting findings is the impact of the Net economy on SMEs and the B2B sector. Here’s how BCG calculates the impact:

In multiple countries—including China, Germany, Turkey, and France—small and medium enterprises (SMEs) that have engaged actively with consumers on the Internet also have experienced three-year sales growth rates up to 22 percentage points higher than those of companies with low or no Internet presence, according to the report.