Visitors to Google’s homepage in the U.S., U.K., and possibly France today were greeted with an interactive, mouse-thwarting bouncing-ball logo that helped knowledge workers master the art of time-suckage. Only no one really knows what it’s supposed to be commemorating. Google denies that the logo is part of a birthday celebration. Search Engine Land speculates we’ll find out more about it at Google’s big event on innovation tomorrow. Like this weekend’s Buckyballs logo, which Google’s Doodlers used to commemorate the 25th anniversary of the discovery of the buckminsterfullerene molecule, today’s bouncing balls (yes, there is a ball theme) are probably also sucking up all your computing power. One vote in favor of the birthday theory is Ad Age’s discovery of a river of corporate checks flowing into Google’s pocket to finance online ads. (BP spent $3.59 million in June alone.) Or maybe it’s just a way to distract the Justice Department from wondering whether Google’s proposed merger with ITA Software, the engine that powers the most popular airline-booking sites, means bye-bye online-travel industry, hello world domination.