Making it into Yahoo!’s top Obsessions of 2011 requires a combination of factors: a fevered and sustained burst in searches and a viral element that can sometimes transcend the obsession itself.

A famous personality can suddenly inspire a major fixation. Last year, Lindsay Lohan filled that role (in 2011, her rocky climb got her into the Top 10 Searches). This year, Charlie Sheen’s rants made for compulsive online monitoring.

But before “tiger blood” cracked the pop-culture vernacular, “tiger mom” was already a full-blown meme, thanks to Amy Chua’s memoir, “The Battle Hymn of the Tiger Mother” (plus a little help from a Wall Street Journal headline that poked at American anxiety over China’s growing superpower status).

Another book stimulated a different kind of frenzy: Book five of the epic fantasy saga “Game of Thrones” sold nearly 300,000 copies on day one. The series also got the HBO treatment, which attracted millions of viewers, 13 Emmy nominations, and a host of YouTube salutes.

Not all YouTubers were so kind: Rebecca Black’s ditty “Friday” quickly won (dis)honors for most hated music video. Its hapless 13-year-old singer received death threats, but more than 200 million views eventually paid off with an album for Black — and a shared moment with Katy Perry.

Must-search topics weren’t all frivolous. The stuck housing market accounted for a very stuck economy. To entice buyers, mortgage rates dropped — and dropped and dropped, down to record lows of 3.94% for 30-year fixed loans and even lower for 15-year mortgages. Financial woes plus a TLC show contributed to a fascination with extreme couponing. While citizens tried to pinch pennies, they grumpily monitored the political bickering that almost brought the whole world to a halt, prompting “government shutdown” searches.

One obsession paid off for Finnish company Rovio: The Angry Birds game was downloaded millions of times, decorated a thousand birthday cakes, and became the year’s hot Halloween costume. In a tough year, that was one of the phenomenal successes that seemed to make life worth living. That, and the world escaping Judgment Day not once but twice, despite predictions from Family Radio evangelist Harold Camping. A close escape like that was enough to make one want to lie face-down and plank.

Intrigued? Obsessed, even? Read on about what preoccupied us in 2011.

The Yahoo! Year in Review editorial lead for five years running, Vera H-C Chan dissects news events, pop-culture idiosyncrasies, and online behavior to probe the “why” behind what’s hot online. On Yahoo!, her articles can be found in News, TV, Movies, and her Shine blog Fast-Talking Dame. Across the Net, there are remnants of contributions to a cultural travel guide, martial arts encyclopedia, movie criticism, business profiles, and A&E/features reporting.

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