* Prefects can take points; Ron got it wrong in Order of the Phoenix, which makes him a pretty poor prefect, eh?
* Fred and George Weasley were born on April Fools' day (no joke).
* Ginny Weasley's first name is Ginevra, and she is the first female Weasley born for "several generations," says JKR.
* Arthur Weasley has two brothers.
* Molly Weasley's maiden name is Prewett.
* Crookshanks is half Kneazle.
* The infamous Weasley cousin who was cut from the books was named Mafalda. She was in Slytherin.
* Dean Thomas's father was killed by Death Eaters when he refused to join them. Neither Dean nor his mother know.
* Dean Thomas was named Gary in the first drafts of the Philosopher's Stone.
* Hagrid, Lily, and James were in Gryffindor. (Hagrid was NOT in Hufflepuff.)
* Hogwarts has about a thousand students. (True, that number doesn't seem right, but J.K.R. said so, and she's the boss.)
* James Potter was a Chaser on the Gryffindor Quidditch team (although the movie claimed he was a Seeker).
* Hermione's birthday is September 19th; Ron's is March 1st.
* James Potter inherited lots of money and didn't need a well-paying profession.
* James Potter inherited the Invisibility Cloak from his father.
* Witches and wizards have longer life-spans than Muggles.
* The Gringotts' goblins return the Muggle money they acquire back into circulation.
* The approximate value of a Galleon is about five pounds ($7.30 or 8.00 Euro), though the exchange rate varies.
* Dumbledore is 150, McGonagall is 70 (and is really an old softy; she just doesn't act like it), Snape is 35 or 36.
* Hogwarts' school motto, "Draco Dormiens Nunquam Titillandus," means, "Never tickle a sleeping dragon."
* If placed in front of a mirror, the inscription on the Mirror of Erised ("Erised stra ehru oyt ube cafru oyt on wohsi") reads, "I show not your face but your heart's desire."
* The happiest people do not become ghosts (12). (Therefore, we can assume that ghosts are people that died while sad, angry, etc. Myrtle was teased; Nearly Headless Nick didn't have his head completely chopped off; the Bloody Baron was...lonely?)
* The Hogwarts teachers do not stay at Hogwarts during the Christmas holidays. However, Filch, Hagrid, and Dumbledore do.
* A few of the Hogwarts professors have spouses, but that information is restricted for reasons we will find out about later. (5)
* To remove the tail that Hagrid gave Dudley in the hut on the rock, the Dursleys went to a private hospital where the staff was very discreet, and said that a wart had gone out of control. (9)
* Aragog is an Acromantula (see Fantastic Beasts and Where to Find Them). (6)
* Dragons can't be domesticated, no matter what Hagrid thinks. (6)
* There is more to the cats in the story (Crookshanks, Mrs. Figg's cats, Mrs. Norris, etc.) than meets the eye. (9)
* The animal an Animagus turns into is a reflection on his/her personality. (8)
* For Hagrid, keeping dangerous creatures is all about overcoming something that could kill him. (6)
* Azkaban is in a sea north of the North Sea. A very cold sea. (12)
* You can do unfocused and uncontrolled magic without a wand (like when Harry blows up Aunt Marge), but to perform really good spells, you need a wand. (5)
* Muggle education is not required for wizard children prior to attending Hogwarts. (9)
* A magical quill detects the birth of every magical child and records it in a book and Professor McGonagall sends an owl to each child when he or she turns eleven. (14)

from http://www.mugglenet.com/books/general_facts.shtml