Facebook is set to pass Yahoo in 2011, capturing 21.6% of all US online display dollars, according to eMarketer. The number is impressive on its own, particularly since only two years ago, Facebook had developed a huge audience but still had almost no revenue to show for it.

However, 21.6% doesn’t tell the whole story. Facebook is even more important to marketers. Display ad revenue doesn’t capture the investment in community management, pages, content, even advertising in apps.

As a platform, an ecosystem and a media property, Facebook is now second only to Google in its importance to media and marketing.