(mostly are bout the characters...)
1.Many mistook Kirito as a girl on the first volume of the novel/manga in Japan.
2.Kirito change his spiky hair in the game and return it to the old one cause Yui thinks it's hard to sit on it.
3.Suguha was meant to be flat chested.(lol her boobs are SUPER BIG now)
4.When the monster in a game presented with "The" it means it's a boss-class monster.
5.Kirito tried to do wield three sword but discontinue it cause he felt his teeth would fall out.
6.The "Sleeping Knights" is a group of terminally ill patients who used the game as form of mental treatment and rehabilitation.(This is Yuuki's group if you don't remember)
7.Yuuki jokingly proposed to Asuna so that she will be named Yuuki Yuuki.(poor Kirito if it happens for real hahaha)
8.3853 died while playing SAO while 6147 survived.
9.There are 10 unique skills in SAO,the six known once are:Infinite Spear,Shurikenjutsu,Bottoujutsu,Darkness Blade,Holy Sword and Duel Wield.
10.There is game like SAO which is "Sword Art Online:Hollow Fragment",the game was sold 145,029 copies on it's first week in Japan.