• by Gavin O'Malley  @mp_gavin, February 9, 2010

Thanks to the ongoing recession, 2009 will go down as the first negative growth year in the history of U.S. e-commerce. That's according to comScore's 2009 U.S. Digital Year in Review, which saw etail spending decrease 2% year-over-year to $209.6 billion.

Weighing down the broader numbers, travel e-commerce spending dropped 5% in 2009 to $79.8 billion, while retail -- non-travel -- e-commerce spending actually remained flat at $129.8 billion.

In stark contrast, most of the last decade was filled with annual etail growth rates in excess of 20% annually, which tapered off by 2008 when the economy began to buckle.

"2009 on the whole fared significantly worse than the previous year with year-over-year growth rates remaining negative throughout most of the year," according to comScore.

That said, the 2009 holiday season represented a bright spot in this largely negative year for e-commerce as it marked a return to positive growth rates, with both November and December showing gains of a few percentage points. Yet, this growth could be attributed to more favorable year-over-year comparisons versus the disastrous 2008 holiday season.

Though few and far between, 2009 did have its winners. In particular, the books and magazines category showed an impressive 12% growth rate, bolstered by category-wide price-cutting and the release of numerous high-profile bestsellers.

Computer software purchases were up 7% online, followed by sport and fitness -- up 6% -- and jewelry and watches -- up 4%.

In the search category, Microsoft sites grew from an 8.3% to 10.7% share of all search queries -- with nearly all of that growth coming in the second half of 2009 subsequent to the software giant launching Bing.

Overall, the U.S. core search market grew 16% in 2009, driven by a 6% gain in unique searchers and a 10% gain in searchers per searcher.

Despite its well-established leadership position, Google Sites' search query volume still managed to grow 21%, driven both by gains in searches per searcher -- up 10% -- and unique searchers -- up 9%.

Led by Facebook and Twitter, social networking established itself as a serious pastime among many Americans. Social networking activity now accounts for 11% of all time spent online, while 4 out of 5 Web users visited one network or another in December.

Facebook finished the year with 112 million visitors in December -- up 105% year-over-year. Twitter finished with nearly 20 million visitors -- up from just 2 million visitors from the previous year. In addition to its surging membership, Facebook grew substantially across nearly every performance metric in 2009. Unique visitors, page views, and total time spent all increased by a factor of two or more.

During the year, the demographic compositions of Facebook, MySpace and Twitter both shifted and cemented. MySpace saw its user composition shift toward younger audience segments in 2009, with people age 24 and younger now comprising 44.4% of the site's audience, while Facebook was evenly split between those younger and older than 35 years of age.

For Twitter, all demographic segments achieved substantial gains in visitors, but certain segments grew more rapidly than others to gain in terms of their share of audience. The initial success of Twitter was largely driven by users in the 25- to-54-year-old age segment, which made up 65% of all visitors to the site in December 2008, with 18- to-24-year-olds accounting for just 9% of visitors.

Later in the year, as Twitter gained widespread popularity with the help of celebrity Tweeters and mainstream media coverage, younger users flooded to the site in large numbers, with those under age 18 -- up 6.2 percentage points -- and 18- to-24-year-olds -- up 7.9 percentage points -- representing the fastest-growing demographic segments.

In 2009, U.S. Internet users viewed a total of 4.3 trillion display ads -- standard and non-standard IAB ads, including both static and rich media, but not video -- representing a growth rate of 21% versus a year ago.

These gains were driven by an 8% increase in the number of people exposed to display ads online, and a 12% increase in average frequency.

Mobile phone network providers AT&T and Verizon ranked as the top U.S. online display advertisers in 2009 -- with 84.3 billion impressions and 56.8 billion impressions, respectively.

With regard to online video, 19% more people in the U.S. viewed more videos for longer periods of time in 2009. In December, a full 86% of the total U.S. online population viewed video content.