"'I suppose you wanted to make an entrance, did you?' [...] 'And with no flying car available you decided that bursting into the Great Hall halfway through the feast ought to create a dramatic effect.'" -- Severus Snape
Before the Hogwarts Express leaves, Tonks rescues Harry from the Full-Body Bind Curse put on him by Malfoy. She escorts him to the castle, but Snape come to collect him and he leads Harry into the feast, criticizing Harry all the way. Once inside, Harry discusses his status as ‘The Chosen One’ with those around him and Dumbledore gives his opening speech, announcing that Slughorn will be teaching Potions and Snape teaching Defense Against the Dark Arts. On the way out of the hall, Harry and Ron discuss Malfoy and run into Hagrid, who tells them about Grawp and he leaves them feeling guilty for not taking his class.
Calendar and Dates
The entire chapter takes place the night students arrive at Hogwarts, which is Sunday, 1 September for two reasons: first, this is the case in every book in the series; second, this aligns with the first hardfast date we have - Ron's birthday on Saturday, 1 March the following year (HBP18).
Interesting facts and notes
"I think you were better off with the old one," said Snape, the malice in his voice unmistakeable. "The new one looks weak."
On a first reading, if the reader takes Tonks' Patronus to be an image of Sirius, this dovetails with Snape's malice towards Sirius' memory - and suggests that it carries over onto anyone close to him. The same holds true for Remus Lupin, of course, with an even nastier suggestion of anti-werewolf bigotry (see Snape's behaviour toward Lupin in PA19, and various remarks throughout the series about Lupin's characteristic appearance of being tired and ill).
the long Gryffindor table (which, inconveniently, was the furthest from the Entrance Hall)
A nice tidbit of information to supplement our floor plans for the layout of the Great Hall.
Exceptional character moments
Tonks, whose Patronus has changed due to great emotional upheaval.
Snape's spiteful crack about Tonks' Patronus looking weaker than her previous one.
"You know, I don't believe any House has ever been in negative figures this early in the term: We haven't even started pudding. You might have set a record, Potter."
He hoped very much that they would all assume he had been involved in something heroic, preferably involving a couple of Death Eaters and a Dementor.
"...and Mr. Filch, our caretaker, has asked me to say that there is a blanket ban on any joke items bought at the shop called Weasleys' Wizard Wheezes."
The last time he had met Hagrid's half-brother, a vicious giant with a talent for ripping up trees by the roots, his vocabulary had comprised five words, two of which he was unable to pronounce properly.