In Harry Potter and the Philosopher's Stone, we see at the selection ceremony that Sorting Hat sorts Draco Malfoy into Slytherin even though Professor McGonagall didn't properly put the Hat on Draco's head. Is there a significance for this? Is the feeling (may have used the wrong word) of Slytherin so strong in him?
There have been many instances in the HP universe where the sorting hat has made a decision almost instantly on making contact with the student's head. Draco and his selection to Slytherin is one such case. It could be because of a string of reasons. Prominent among them would be his lineage. He comes from a historically long line of Slytherins.
The Malfoy family consists of an ancient line of pure-blood wizards, most of whom attended Hogwarts School of Witchcraft and Wizardry and were traditionally sorted into Slytherin House. The family first arrived in Britain with Armand Malfoy, who founded the family estate Malfoy Manor on land obtained from King William I.
Thus it's natural for Draco to feel pretty confident about ending up in Slytherin. He even says before the sorting
"I know I´ll be in Slytherin, all our family have been."
This is a pretty big factor but not the only one. If you remember, Sirius ended up in Gryffindor even though the Blacks were all proud Slytherins. This has to do largely with the wizard's own personality and wishes. Sirius did not conform to his family's view of purity and their alignment with the dark powers. However, Draco has no such reservations. He prides his family's pure-blood status and that his father was a prominent Death Eater. He sees himself to grow up to be just like him.
In Harry's case, the sorting hat took an unusually long time since it took Harry's strong desire to not be sorted into Slytherin into account. Even though the Sorting Hat felt he had enough qualities, parseltongue being one of them, to qualify as a bonafide Slytherin.