
As with almost everything here, there is a lot of tradition surrounding hall dining and, as has been pointed out by other Americans in Cambridge, the traditions of a particular College's formal hall can tell you a lot about the character of the College. Unsurprisingly, I've attended the most formals at Churchill, so--to give you a 'taste' of a formal--let me describe formal hall at Churchill.
Formal hall is held at Churchill on Tuesdays, Thursdays and Fridays. Dress code is formal; a suit jacket and tie are required for men and ladies are expected to dress accordingly (usually cocktail dresses).
The meal starts at 7:30pm with the ringing of a gong that signals that hall is open. All diners--other than the fellows and their guests at high table--are expected to take places at the tables quickly. However, protocol dictates that no one sits until after the high table has come in and grace is said. Grace at Churchill takes the form of a quick and painless recitation of the two words 'benedictus benedictat' by the Master, the President of the SCR or whomever is presiding over high table.
The short grace here is telling; the College itself was founded as a secular college and only later was the Chapel at Churchill built at the far end of the grounds near the Institute of Astronomy.
The meal itself begins after everyone has been seated. A typical meal has an appetizer, main course consisting of some sort of meat (unless requested otherwise) accompanied with vegetables (usually potatoes, cabbage and carrots) and dessert. The courses come slowly, encouraging both talking and drinking; by the end of a meal, with alcohol loosening tongues, hall can easily become so noisy that conversation is only really possible with the two diners seated to your immediate right and left.
Shortly after dessert is served, everyone stands as the high table leaves for post-dinner drinks and/or coffee in the SCR. Before sitting again to finish dessert and enjoy a cup of coffee or tea, two toasts are offered, first 'to the Queen' and second 'to Sir Winston!'
The formalities end there. After 10 or so minutes of relative peace, diners deep in conversation are encouraged out of hall by the hall lights being raised and the staff unceremoniously clearing the tables in front of the diners.

Surprisingly, I don't have any pictures of Churchill's hall!
Last night, it wasn't all the tradition that struck me but rather how normal this kind of dining is in the Cambridge university community. As Zoran (one of the lecturers in physics) put it, it's something that you just can't find anywhere else, with the possible exception of the other place.