Serena again re-affirmed her domination of Sharapova, winning her 10th match in 12 meetings (the only losses to the Russian coming in two huge matches, the 2004 Wimbledon final and the 2004 WTA Tour year-end championship match, when Sharapova was a teenage phenom). You read that right, Serena has not lost to the 4-time major champion for 8 long years, and they both know it every time they step on to court together. Playing Sharapova concentrates Serena's mind so that her unforced errors drop precipitously while her deadly accuracy and power remain, a lethal combination which resulted in 40 winners (to a mere 14 errors) in the 89 minute championship match, while never even facing a break point.
But really 2012 was the year the now-31 year old Serena played an entire tour season completely healthy and committed to the game in a long time and the results are clear and convincing. Serena ended up winning 47 of her last 49 matches in 2012 and went on an 11-0 run against the Top 2 players in the world. During that time she won 2 majors and 2 Olympic gold medals.
However, by winning the year-end championships for the 3rd time at age 31, Serena became the oldest player to ever win the tournament and joined Steffi Graf, Martina Navratilova, Monica Seles, Kim Clijsters and Chris Evert as 3-time winners. She joined Victoria Azarenka as the only other player to win $7 million in a season.
As long as she remains healthy there is no reason to think that Serena will not continue her domination of women's tennis for at least the next year or two, which should allow her to reach (and possibly even surpass) the 18 majors that Evert and Navratilova share. Graf's total of 22 should be safe. Probably.