A man-made disaster, a global sport, pop culture’s leading ladies (and one young gent), and gadgets starting with an “i.”

Since 2001, Yahoo! has been tallying up the top searches of the year, providing a snapshot of a culture in motion. Over the past decade, the No. 1 slot has been occupied by companies (music download service Kazaa), TV shows (“American Idol”), and celebrities (Britney Spears, often). In 2010, some 631 million people checked in. Among the billions of queries they pursued, the story of the Gulf of Mexico oil spill led the year’s top 10 — the first time that a news story has taken the No. 1 slot.

Following the Deepwater Horizon oil rig explosion that killed 11 on April 20, the gushing crude took 86 days to cap. The live feed from the ocean floor became must-watch viewing, as massive online scrutiny monitored best (and not so best) efforts to kill the well and stop the worst spill in marine history. Besides igniting the issue of workplace safety, the disaster became a lightning rod for people’s feelings about America’s energy policies, big government, billionaire CEOs, environmental protection, and technological safety.

Another event did distract from the drama 5,000 miles deep in the Macondo Prospect. South Africa, the first African nation to host the FIFA World Cup, welcomed 32 nations in a global tournament of men’s soccer. People took an online crash course in the sport, learning about the rules of the game, the major players (and outrageous referees), the octopus oracle, and native horns that just wouldn’t quit. The summer break brought productivity to a standstill and landed the World Cup in second place on our top 10 searches.

Dizzying tech advances belied a bad economy. The iPhone‘s fourth coming captivated naysaying geeks and covetous consumers alike, and beat out the iPad in searches. An accidental sneak peek unfolded like a joke (“So this engineer walks into a bar…”), but ended in record lines at stores. High-tech drama stimulated an already frenzied Mac cult (which was also tracking the Apple iPad), and pushed the iPhone into the No. 6 slot.

Filling out the other top 10 spots? Guilty pleasures like “American Idol,” the Web-spun music artist Justin Bieber (in his first top 10 appearance), and a bevy of pop culture’s young leading ladies — Megan Fox, Kim Kardashian, Lady Gaga — who could give lessons in the art of the manufactured self.

What’s notable isn’t just what commanded people’s online vigilance the most, but who almost dropped from the list. For years Britney Spears dominated the top 10, but she tumbled from her No. 1 spot to No. 5 in 2009. This year — a relatively quiet one for the music superstar — she hung in at No. 10.

Is the end near for Spears? Don’t count her out yet. Dive deep into the top searches and stories of 2010, and get a glimpse at what lies ahead.

–Vera H-C Chan

Yahoo! Year in Review editorial lead for four years running, Vera H-C Chan dissects news events and search trends to share the why behind what’s hot online and in the media. On Yahoo! her writing can be found all over, including in Buzz Log, TV, Movies, and her Shine blog Fast-Talking Dame.